feat(terminal): Auto Copy, put a finished selection on the clipboard

App Settings > Terminal & Input > Selection & clipboard > Auto Copy
Selection (`autoCopySelection`, per-device, default OFF). With it on,
highlighting text in the terminal copies it: mouse drag, double-click
word, triple-click line, and the phone long-press selection. Ctrl+C is
untouched and still copies on demand.

Three things decide the shape of it:

* It fires at the END of a gesture, never in onSelectionChange. That
  callback runs for every cell a drag crosses, so copying there would be
  one clipboard write per mouse move. It only arms a pending flag; a
  document-level mouseup listener flushes, and the touch path calls the
  flush itself because it preventDefaults its touchend and no mouseup
  ever arrives there.
* The flush is synchronous inside the handler, because both clipboard
  paths need user activation: Firefox gates navigator.clipboard
  .writeText on it, and execCommand('copy'), the fallback the plain-HTTP
  LAN install lands on, has to run in the gesture's own task. A timer or
  a wait for onSelectionChange loses it, invisibly in Chrome.
* It deliberately does NOT do what copyTerminalSelection() does. That
  one clears the selection (so a second Ctrl+C is an interrupt) and
  focuses the terminal. Clearing would make text vanish under the cursor
  that just highlighted it, and focusing opens the on-screen keyboard
  over it on a phone. Focus is instead restored to whatever held it,
  which only matters for the execCommand fallback.

Guards are pure in decideAutoCopy() (constants.js): off, blank or
whitespace-only text, and a 1M-char cap, since a drag off the top of the
viewport autoscrolls and one gesture can sweep the whole 50k-line
scrollback. Past the cap the copy is refused rather than truncated, with
a toast pointing at Ctrl+C.

Feedback is silent on success except once per page load, so a feature
that works by doing nothing visible can still be told from a dead
toggle; failures and refusals toast, throttled to 10s.

Per-device on both counts the settings rule requires: in `displayKeys`
and absent from the .strict() SettingsUpdateSchema, because clipboard
access differs by device and by origin.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/wiki/Settings-Reference.md

@@ -45,6 +45,7 @@ supervised by systemd or launchd; npm installs report as non-updatable. See
 | CJK Input                     | Off                  | IME composition through a dedicated text field.                        |
 | Extended Keyboard Bar         | Per device           | Which accessory bar phones get. Shell sessions override it while they are active. |
 | Wheel Scrolls Local History   | Off                  | Keeps the wheel on the local buffer instead of forwarding it to the CLI. |
+| Auto Copy Selection           | Off                  | Copies highlighted terminal text to the clipboard the moment you finish selecting it. Ctrl+C still copies on demand. |
 | WebGL Renderer                | On                   | With a GPU-stall watchdog that falls back to DOM rendering.            |
 | Gesture Control               | Off                  | Camera hand tracking. Also needs `CODEMAN_GESTURE=1` on the server.    |