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>

src/web/public/settings-ui.js

@@ -381,6 +381,10 @@ Object.assign(CodemanApp.prototype, {
     document.getElementById('appSettingsTunnelEnabled').checked = settings.tunnelEnabled ?? false;
     this.loadTunnelStatus();
     document.getElementById('appSettingsLocalEcho').checked = settings.localEchoEnabled ?? MobileDetection.isTouchDevice();
+    // Auto Copy (copy-on-select): per-device, default OFF everywhere. It quietly
+    // overwrites the system clipboard on a gesture the user may have meant only as
+    // a way to read, so it is opt-in rather than a default anyone has to discover.
+    document.getElementById('appSettingsAutoCopySelection').checked = settings.autoCopySelection === true;
     document.getElementById('appSettingsTerminalFont').value = settings.terminalFontFamily || '';
     document.getElementById('appSettingsTerminalWheelLocal').checked =
       settings.terminalWheelLocalScrollback ?? defaults.terminalWheelLocalScrollback ?? false;
@@ -2007,6 +2011,7 @@ Object.assign(CodemanApp.prototype, {
       imageWatcherEnabled: document.getElementById('appSettingsImageWatcherEnabled').checked,
       tunnelEnabled: document.getElementById('appSettingsTunnelEnabled').checked,
       localEchoEnabled: document.getElementById('appSettingsLocalEcho').checked,
+      autoCopySelection: document.getElementById('appSettingsAutoCopySelection').checked,
       terminalFontFamily: document.getElementById('appSettingsTerminalFont').value.trim(),
       terminalWheelLocalScrollback: document.getElementById('appSettingsTerminalWheelLocal').checked,
       cjkInputEnabled: document.getElementById('appSettingsCjkInput').checked,
@@ -2203,6 +2208,11 @@ Object.assign(CodemanApp.prototype, {
       showFileViewerButton: _fvb,
       webglRendererEnabled: _wgl,
       terminalWheelLocalScrollback: _twls,
+      // Copy-on-select. Per-device (clipboard access differs by device and by
+      // origin: the plain-HTTP LAN install has no navigator.clipboard at all)
+      // and absent from SettingsUpdateSchema (.strict()), so sending it would
+      // 400 the whole settings PUT.
+      autoCopySelection: _acs,
       // Per-device by nature (the font must exist on the device) and absent
       // from SettingsUpdateSchema (.strict()) — sending it would 400 the PUT.
       terminalFontFamily: _tff,
@@ -2883,6 +2893,7 @@ Object.assign(CodemanApp.prototype, {
           'terminalFontFamily',
           'language',
           'terminalWheelLocalScrollback',
+          'autoCopySelection',
           'showSessionButton', 'showAwayDigestButton', 'showCronButton',
           'showTabDetachButton',
           'mobileOverviewEnabled',