phone app: installable, opens offline, takes the share sheet onto the scratchpad, back lets go of one thing

A manifest with a 192, a 512 and a maskable icon, and a hand-written service
worker built beside the app by a small vite plugin: it keeps index.html, the
logo, the entry with its imports and the latin fonts, keeps each hashed asset
once fetched, asks the server for pages first and answers from the cache when
it is down, and never touches /api. The CSP names worker-src and manifest-src.

The share target posts to /share, which the worker catches: the text waits in
a cache and becomes a scratchpad note once someone is logged in, with the
drawer down on it. On a touch screen one guard entry in the history makes back
let go of one thing at a time — a prompt, the line, a sheet, the drawer, the
editor, a tile, then a folder up — and leave only at a space's root. The bar
and the band grow by the safe-area insets. The login no longer says the server
is unreachable once it answers again with the session gone.

docs/wiki/Capture.md

@@ -60,3 +60,8 @@ with a text-input variable, method `POST`, the same header, and a JSON body
 `{"text": "{{input}}"}`.
 
 Either one can sit on the home screen, or behind the share sheet.
+
+**Android, without a token**: install the workspace from Chrome (*Install app*,
+over HTTPS) and it is in the share sheet itself. What is shared to it — a link,
+some text, a title — becomes a note on the scratchpad, from the session the app
+is logged in with. See [On a phone](Guide.md#on-a-phone).