own /effort: respawn-with-resume carrying --effort, picker UX (T-412)

Spike result (probed claude 2.1.175 over stream-json): there is NO
set_effort/set_thinking_effort control subtype — both are rejected. The
lever is the `--effort <level>` spawn flag (low/medium/high/xhigh/max;
settings.json effortLevel is the persisted default). So changing effort
restarts the process: respawn-with-resume keeps the conversation and
carries the flag — the same continuity /clear and /resume already rely on.

- SpawnSpec.effort → orchestrator appends `--effort <level>`.
- claude_pane: /effort <level> validates and respawns (toast explains the
  restart); bare /effort opens a picker; the pane re-applies its effort on
  every later respawn. Invalid level → local notice listing levels.
- ModelPickerCard generalised minimally (title + isCurrent predicate) so
  the effort picker reuses it; effort needs exact matching because `high`
  is a substring of `xhigh` and alias-containment would mis-mark it.
- SessionStatus.effort + StreamJsonSession.noteEffort: the wire never
  reports effort, so the spawner records what it set; status/sidebar read
  it from the normal status stream.
- Routing: effort moves from the TUI-only catalog to kClideOwnedCommands.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/builtin/claude/stream_json_session_test.dart

@@ -640,6 +640,15 @@ void main() {
     expect(statuses.last.permissionMode, 'plan', reason: 'only ExitPlanMode exits plan mode');
   });
 
+  test('noteEffort merges the effort level into the status (T-412)', () async {
+    proc.emit(initEvent());
+    await Future<void>.delayed(Duration.zero);
+    session.noteEffort('xhigh');
+    await Future<void>.delayed(Duration.zero);
+    expect(statuses.last.effort, 'xhigh');
+    expect(statuses.last.model, 'claude-opus-4-7'); // merge, not replace
+  });
+
   test('addLocalNotice emits a synthetic clide item and sends nothing (T-411)', () async {
     final before = proc.writes.length;
     session.addLocalNotice('/status is a Claude Code TUI command');