feat(shortcuts): user-configurable keyboard shortcuts for session actions

Adds a keyboard shortcut feature (Rust matcher + Dart UI + cross-language
  parity tests) that lets users bind combinations like Ctrl+Alt+Shift+P to
  session actions. Bindings are stored in LocalConfig under
  `keyboard-shortcuts`; the matcher gates dispatch on `enabled` and
  `pass_through` flags so flipping the master switch off is a hard stop.

  Wire-up summary:
  - src/keyboard/shortcuts.rs: matcher, default bindings, parity test against
    flutter/test/fixtures/default_keyboard_shortcuts.json
  - src/keyboard.rs: shortcut intercept in process_event{,_with_session},
    feature-gated to `flutter`; runs before key swapping so users bind to
    physical keys
  - src/flutter_ffi.rs: main_reload_keyboard_shortcuts +
    main_get_default_keyboard_shortcuts; reload_from_config seeded in main_init
  - flutter/lib/common/widgets/keyboard_shortcuts/: shared config page body,
    recording dialog, shortcut display formatter, action group registry
  - flutter/lib/desktop/pages/desktop_keyboard_shortcuts_page.dart and
    flutter/lib/mobile/pages/mobile_keyboard_shortcuts_page.dart: platform
    shells around the shared body
  - flutter/lib/models/shortcut_model.dart: per-session ShortcutModel +
    registerSessionShortcutActions for actions with no toolbar TToggleMenu /
    TRadioMenu (fullscreen, switch display/tab, close tab, voice call, etc.)
  - flutter/lib/common/widgets/toolbar.dart: optional `actionId` field on
    TToggleMenu / TRadioMenu, plus per-helper auto-register pass that wires
    tagged entries' existing onChanged into the ShortcutModel
  - flutter/test/keyboard_shortcuts_test.dart + fixtures: cross-language
    parity (default bindings, supported key vocabulary)

  Design principles applied during review:

  1. Additions are fine; modifications to original logic must be deliberate.
     Tagging an existing TToggleMenu entry with `actionId:` is an addition.
     Rewriting its onChanged to satisfy a new contract is a modification —
     and was reverted for every case where the original click behavior was
     working. Four closures were touched and then reverted (mobile View
     Mode, Privacy mode multi-impl, Relative mouse mode, Reverse mouse
     wheel); their shortcuts are wired via standalone closures in
     shortcut_model.dart instead.

  2. Toolbar auto-register is reserved for entries whose onChanged is
     inherently self-flipping — typically `sessionToggleOption(name)` where
     the named option is flipped in place and the input bool is unused. The
     register pass passes `!menu.value` from registration time, which is
     harmless under self-flipping but wrong for closures that consume the
     input bool directly. Tagging a non-self-flipping entry forces a closure
     rewrite; choose non-toolbar registration in that case.

  3. When shortcuts are disabled, toolbar behavior must be bit-for-bit
     unchanged. The matcher's `enabled`-gate already guarantees no
     dispatch; the auto-register pass is left unconditional (its only effect
     is HashMap operations on a separate ShortcutModel) so mid-session
     enable works without a reconnect. The trade-off is intentional and
     documented at the top of toolbarControls.

  4. Comments stay terse. Rationale lives in one place — the doc comment of
     the helper or registration site, not duplicated at every call site.

  5. Where an existing helper needs a new optional behavior (e.g.
     `_OptionCheckBox` gaining a tooltip slot), the new branch must reduce
     to byte-identical output for existing callers (`trailing == null`
     case → original `Expanded(Text)` layout). Verified.

  6. Action IDs and labels stay consistent. Renamed `reset_cursor` →
     `reset_canvas` so the action ID matches its user-facing label
     ("Reset canvas") and capability flag.

  Out-of-scope but included:
  - AGENTS.md: documents flutter_rust_bridge no-codegen workflow and the
    Web target's hand-written TS client, since both are load-bearing for
    any new FFI work.
  - remote_toolbar.dart: i18n fix for the per-monitor tooltip ("All
    monitors" / "Monitor #N"), unrelated to shortcuts but kept here.

flutter/lib/mobile/pages/mobile_keyboard_shortcuts_page.dart

@@ -0,0 +1,95 @@
+// flutter/lib/mobile/pages/mobile_keyboard_shortcuts_page.dart
+//
+// Mobile shell for the Keyboard Shortcuts configuration page. Mirrors
+// `desktop/pages/desktop_keyboard_shortcuts_page.dart` but with a touch-
+// friendly layout (ListTile rows instead of dense rows) and a hint banner
+// that explains the recording flow only works with a physical keyboard.
+//
+// All actual logic — group definitions, JSON I/O, conflict-replace flow,
+// recording-dialog round-trip, "Reset to defaults" — lives in the shared
+// `common/widgets/keyboard_shortcuts/page_body.dart`. This file only
+// supplies the AppBar, the AppBar action, and the platform hint banner.
+//
+// Mobile keyboard detection limitation: Flutter has no reliable
+// "is a physical keyboard attached?" API on iOS or Android. Soft keyboards
+// don't generate the `KeyDownEvent`s the recording dialog listens for, so
+// in practice the dialog only does anything useful when the user actually
+// has a hardware keyboard plugged in (USB / Bluetooth / Smart Connector).
+// For V1 we don't try to detect attachment — we just surface the
+// requirement as an in-page hint instead of disabling the Edit button.
+
+import 'package:flutter/material.dart';
+
+import '../../common.dart';
+import '../../common/widgets/keyboard_shortcuts/page_body.dart';
+
+class MobileKeyboardShortcutsPage extends StatefulWidget {
+  const MobileKeyboardShortcutsPage({Key? key}) : super(key: key);
+
+  @override
+  State<MobileKeyboardShortcutsPage> createState() =>
+      _MobileKeyboardShortcutsPageState();
+}
+
+class _MobileKeyboardShortcutsPageState
+    extends State<MobileKeyboardShortcutsPage> {
+  final GlobalKey<KeyboardShortcutsPageBodyState> _bodyKey = GlobalKey();
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    return Scaffold(
+      appBar: AppBar(
+        title: Text(translate('Keyboard Shortcuts')),
+        actions: [
+          IconButton(
+            tooltip: translate('Reset to defaults'),
+            onPressed: () =>
+                _bodyKey.currentState?.resetToDefaultsWithConfirm(),
+            icon: const Icon(Icons.restore),
+          ),
+        ],
+      ),
+      body: KeyboardShortcutsPageBody(
+        key: _bodyKey,
+        compact: false,
+        editButtonHint: translate('shortcut-mobile-physical-keyboard-tip'),
+        headerBanner: _PhysicalKeyboardHintBanner(theme: theme),
+      ),
+    );
+  }
+}
+
+/// A muted info banner shown above the master toggle on mobile. We can't
+/// reliably detect whether a physical keyboard is attached, so instead of
+/// disabling the Edit button we surface the requirement up front.
+class _PhysicalKeyboardHintBanner extends StatelessWidget {
+  final ThemeData theme;
+  const _PhysicalKeyboardHintBanner({required this.theme});
+
+  @override
+  Widget build(BuildContext context) {
+    final color = theme.colorScheme.primary.withOpacity(0.08);
+    return Container(
+      padding: const EdgeInsets.all(12),
+      decoration: BoxDecoration(
+        color: color,
+        borderRadius: BorderRadius.circular(8),
+      ),
+      child: Row(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          Icon(Icons.info_outline,
+              size: 18, color: theme.colorScheme.primary),
+          const SizedBox(width: 8),
+          Expanded(
+            child: Text(
+              translate('shortcut-mobile-physical-keyboard-tip'),
+              style: TextStyle(color: theme.colorScheme.onSurface),
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}

flutter/lib/mobile/pages/remote_page.dart

@@ -127,10 +127,10 @@ class _RemotePageState extends State<RemotePage> with WidgetsBindingObserver {
       // what we want here.
       if (mounted) {
         toolbarControls(context, widget.id, gFFI);
-        // Mobile has no DesktopTabController, so tab-switch shortcuts
-        // remain unregistered (they will simply log a no-handler debug
-        // line if a mobile user binds one — they have no tabs to switch).
+        // Mobile has no DesktopTabController, so tab-switch shortcuts will
+        // log a no-handler debug line if a user binds one.
         registerSessionShortcutActions(gFFI);
+        registerToolbarShortcuts(context, widget.id, gFFI);
       }
     });
     WidgetsBinding.instance.addObserver(this);