fix(agents): stop falsely reporting saved agent edits on external OpenCode; make model-selector shortcut customizable (#1839)

* feat(shortcuts): make 'Open model selector' shortcut customizable

Lets users remap the model selector shortcut (e.g. to Ctrl+M) via
Settings > OpenChamber > Shortcuts, matching OpenCode's quick
model-switch keybinding workflow.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* fix(agents): surface manual-restart needed when on external OpenCode

Agent prompt/permission/settings edits are written to disk, but an
external OpenCode server (skip-start or auto-detected on the default
port) is not owned by OpenChamber and is only health-probed on config
change, so it keeps serving its startup-cached config until restarted.
The API previously claimed a successful reload, so the UI silently
reverted the edit to the stale/default value on refresh.

Now refreshOpenCodeAfterConfigChange reports whether a real reload
happened; agent routes return requiresManualRestart for external mode;
and the agents UI keeps the saved values and warns the user to restart
their OpenCode server instead of showing a false success. Managed mode
behavior is unchanged (process is restarted and reload is live).

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

---------

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/lib/shortcuts.ts

@@ -291,6 +291,7 @@ const SHORTCUT_ACTIONS: ReadonlyArray<ShortcutAction> = [
     defaultCombo: 'mod+shift+m',
     label: 'Open model selector',
     description: 'Open model selector while in chat',
+    customizable: true,
   },
   {
     id: 'cycle_thinking_variant',