docs: a guide, a wiki and screenshots

The README grew a section per feature and is a good reference, but nothing
said where to begin. docs/wiki now has a getting-started page, a guide that
walks through one day with the workspace and explains each part where it comes
up, and a page per part of the app, each with screenshots of what it
describes.

Three pages are read out of the code rather than written, so they cannot drift
from it: the keys and commands from Help.svelte and commands.ts, the same lists
`:help` draws; the settings from .env.example, which gains a heading for the
vault, trash and history settings so they no longer sit under mail; and the
API from the README's table. `make wiki` writes them, and `--check` fails when
one is stale or a link between pages leads nowhere. `--publish` lays the pages
out for a GitHub wiki: links without `.md`, images beside them, `[[` escaped so
the wiki does not take a command's help text for a link to a page.

The screenshots are taken by `make screenshots`: the debug binary on a
temporary data directory, with a password made up for the run, filled with an
example workspace over the API, and a headless Chromium driven over the
DevTools protocol through the views the docs show. Nothing outside the
temporary directory is touched but docs/images, and the pictures are cut to
256 colours, a third of their size, which a dark UI does not show.

The README opens with the banner, a CI badge, the guide, the features grouped
by what they are for, and six of the screenshots.

docs/wiki/Guide.md

@@ -0,0 +1,183 @@
+# The guide: a day with the workspace
+
+This page follows one ordinary day: the agenda in the morning, notes and cards
+at work, a lecture in the afternoon, a thought on the way home, and the diary in
+the evening. Each part of the workspace is explained where it first comes up,
+with a link to the page that has the rest of it.
+
+The keys are the desktop's. On a phone, every one of these has a button; see
+[On a phone](#on-a-phone) at the end.
+
+## Morning: what needs you
+
+The first time you open the workspace each day, the **agenda** opens by itself
+when anything is late or due. Any other time, press `t`.
+
+![The agenda](../images/agenda.png)
+
+It gathers the unfinished cards of every board into four groups:
+
+- **late**: past their due date;
+- **today**: due today;
+- **this week**: due in the next seven days;
+- **in hand**: in a list between the inbox and done, which means work has
+  started on them.
+
+Under the cards it says whether the diary has an entry for today, and lists
+what you wrote on this day in earlier years.
+
+Walk it with `j` and `k`. On a card:
+
+- `Space` finishes it, where it stands;
+- `D` gives it a due date: `fri`, `tm`, `+3d`, `10-31`;
+- `H` and `L` move it to the list left or right on its board;
+- `Enter` goes to the card on its own board.
+
+`Esc` or `t` closes the agenda. The bar keeps showing the `late` and `today`
+counts while either is above zero. More in [Boards and the agenda](Boards-and-Agenda.md).
+
+## At work: spaces, documents and tiles
+
+Press `2` for the `work` space. A **space** is one area of your life, with its
+own folders, its own board and its own search. Make more with
+`:space! <name>`; `w` shows all of them at once, with what was last written in
+each.
+
+![Every space at a glance](../images/overview.png)
+
+The list on the left shows the folder you are in. `j` and `k` move, `l` or
+`Enter` opens what is under the cursor, `h` goes up a level. Folders come first,
+then documents grouped by the day they were written.
+
+Open the project notes with `Enter`. To read a second document beside it, move
+to it and press `L` instead: it opens in a **tile** of its own.
+
+![Two documents in tiles](../images/tiles.png)
+
+`Alt-h` and `Alt-l` move between the tiles and back to the list, `Alt-q`
+closes one, and `f` makes the focused one fill the screen. Each space remembers
+its tiles, so switching away and back finds them as they were. More in
+[Spaces and documents](Spaces-and-Documents.md).
+
+### Writing
+
+`i` edits the open document. The editor is CodeMirror with real vim keys:
+`ciw`, `dd`, visual mode, macros, `.` and the rest. `Esc` leaves insert mode,
+and `:q` leaves the editor.
+
+![The editor](../images/editor.png)
+
+The document is markdown. Tables, code blocks, task lists and
+math (`$x^2$`, or `$$…$$` on its own) are drawn when you read it. Link to
+another document by its title, `[[Runbook]]`; typing `[[` offers the titles to
+pick from. When the other document is renamed or moved, the link is rewritten
+to follow it.
+
+You do not need to save. Every keystroke goes to the browser's storage at
+once, and to the server a couple of seconds after you stop typing. If the
+network is gone, the draft waits in the browser and is sent when it comes back.
+More in [Writing](Writing.md).
+
+### Cards
+
+In a meeting someone asks you to renew a certificate. Press `c`, type
+`Renew the gateway certificate`, and `Enter`. The card is in this space's
+inbox, and you have not left the document you were reading.
+
+Press `b` to see the **board**.
+
+![The board](../images/board.png)
+
+The first list is the inbox and the last is done; the ones between are work in
+hand. `h`/`l` move between lists and `j`/`k` between cards. `H`/`L` move a
+card across, `Space` finishes it, `D` sets its due date, and `Enter` opens its
+notes: a document made for the card the first time you ask. `:repeat weekly`
+makes a card come back in the inbox each time it is finished. `q` goes back to
+the tree.
+
+### Finding things
+
+`/` searches the space you are in, as you type. `Ctrl-P` searches every space.
+The search reads the documents and the text files in the tree: a log file is
+found by a line inside it, and the result shows the words around the match.
+
+![A search that found a log line](../images/search.png)
+
+`Tab` walks the results without leaving the line, `Enter` opens one, and
+`n`/`N` step through them afterwards. More in [Files and search](Files-and-Search.md).
+
+## Afternoon: a lecture
+
+Press `3` for `uni`. The lecture notes have formulas in them, written as
+LaTeX between dollar signs and drawn by KaTeX:
+
+![Math in a document](../images/math.png)
+
+The slides came as a PDF. Drop it onto the list, or `:upload`, and it is a
+file in the folder, beside the notes about it. `Enter` opens a PDF, an image, a
+video, a CSV table, a text or source file, or a certificate in place. Anything
+else downloads with `:dl`.
+
+![A CSV file as a table](../images/file-table.png)
+
+A scan of something private, like an ID or a contract, goes in with
+`:upload!` instead. That seals it in the **vault**, under a password that is
+never stored. See [The vault](Vault.md).
+
+## On the way home: capture
+
+A thought arrives when no tab is open. `:token add phone` makes a token. With
+it, an iPhone Shortcut, an Android HTTP Shortcut or a single `curl` puts a card
+in an inbox, or a line in today's diary entry:
+
+```sh
+curl -H "Authorization: Bearer nwc_…" -H 'content-type: application/json' \
+  -d '{"text":"call the bank"}' https://your-host/api/capture
+```
+
+The token can do this and nothing else. See [Capture](Capture.md).
+
+## Evening: the diary
+
+Press `T` for today's entry. If there is none yet it is started, from the
+diary's `templates/day` document when there is one, and opens ready to write.
+
+`C` shows the diary by month. A dot marks a day with an entry; `h`/`l`,
+`j`/`k` and `H`/`L` move by day, week and month, and `Enter` opens the day,
+or starts an entry for it. In an entry, `[d` and `]d` step to the one before
+and after.
+
+![The diary by month](../images/calendar.png)
+
+If nothing was written in the diary by the evening and mail is set up, a
+reminder arrives at `WORKSPACE_REMINDER_AT`. More in [The diary](Diary.md).
+
+## When something goes wrong
+
+- **Deleted the wrong thing?** `u` brings the last delete back. `:trash` lists
+  everything deleted in the last 30 days.
+- **Overwrote a paragraph?** `gh` lists the document's earlier versions as diffs
+  against the text as it is now, and `Enter` brings one back.
+
+  ![Earlier versions of a document](../images/history.png)
+
+- **Saved in two places?** A document saved somewhere else since you opened it
+  is not overwritten: `:w` says so, `:e!` takes the other version, and `:w!`
+  writes yours anyway.
+
+More in [Not losing things](Not-Losing-Things.md).
+
+## On a phone
+
+On a touch screen the workspace drops the modal keys, and under 768 pixels
+wide the list and the open document take the whole screen in turn. A dock along
+the bottom has a new document, a new folder, the board, today's entry, an
+upload, the trash and a search. The `⋯` on a row, or a long press, has
+everything that can be done to it: rename, move, share, seal, delete. The agenda
+has a done button on each card.
+
+| | |
+| --- | --- |
+| ![The tree on a phone](../images/mobile-tree.png) | ![A document on a phone](../images/mobile-document.png) |
+
+`:set vim` turns the vim keys on for a phone with a keyboard.