keys: one table drives dispatch, help, footers, the rail and the wiki

keymap.ts lists every key with its context, action and help line.
actions.ts holds what each one does, typed against the table so a key
without an action, or an action without a key, does not compile.
modes.ts stacks the contexts (always > sheet > drawer > workspace >
writing > focused tile > special > global) and writes the two-key
pending logic once. App.svelte's 480-line onkeydown is now one call.

Help, the panel footers (a shared Keys component), the rail's keycaps
and Commands.md all read the table; the wiki gains the card and
scratchpad key tables.

One fix on the way: Ctrl-S in the editor no longer saves twice, which
could make the second save fail as "changed somewhere else".

docs/wiki/Development.md

@@ -28,7 +28,8 @@ real data stays out of it.
 | `src/vault.rs` | the vault's keys and file format |
 | `src/sweep.rs` | the daily clean-up: trash, old versions, unreferenced uploads |
 | `migrations/` | the SQLite schema, one numbered file per change |
-| `web/src/App.svelte` | the keys |
+| `web/src/lib/keymap.ts` | every key: where it is heard, what it is called, its help line |
+| `web/src/lib/actions.ts`, `modes.ts` | what each key does, and which contexts hear it first |
 | `web/src/lib/store.svelte.ts` | the client's state, and every call to the API |
 | `web/src/lib/commands.ts` | the `:` commands |
 | `web/src/lib/Help.svelte` | the `?` screen |
@@ -78,7 +79,7 @@ Three pages are generated by `scripts/wiki.ts`:
 
 | page | read from |
 | --- | --- |
-| [Keys and commands](Commands.md) | `web/src/lib/Help.svelte` and `web/src/lib/commands.ts` |
+| [Keys and commands](Commands.md) | `web/src/lib/keymap.ts` and `web/src/lib/commands.ts` |
 | [Configuration](Configuration.md) | `.env.example` |
 | [API](API.md) | the API section of `README.md` |