…oller.py -> specter_gui.py)

The class and module name NavigationController was too generic and didn't
reflect the role of this central UI object. SpecterGui better expresses
that this is the top-level GUI root for the Specter device UI.

- Renamed basic/navigation_controller.py to basic/specter_gui.py
- Renamed class NavigationController to SpecterGui throughout
- Updated all imports, __all__ exports, comments and docstrings
- Updated README docs and MOCKUI_PROGRESS.md

…implementations

The classes in helpers/ (UIState, SpecterState, Battery, Wallet) are
stub implementations that will later be replaced by real Specter business
logic. Renaming to stubs/ makes that intent explicit.

- Renamed MockUI/helpers/ directory to MockUI/stubs/
- Updated all imports across basic/, wallet/, __init__.py and tests/

…rthands

TitledScreen now exposes self.gui (the SpecterGui root) instead of
self.parent, avoiding confusion with LVGL's widget parent concept.

Subclasses should use:
  self.gui   - for SpecterGui-specific methods (show_menu, refresh_ui,
               ui_state, keyboard_manager, change_language)
  self.state - shorthand for gui.specter_state (no bypass)
  self.i18n  - shorthand for gui.i18n (no bypass)
  self.on_navigate - shorthand for gui.on_navigate (no bypass)

- Removed redundant setattr(self.parent.specter_state, ...) in
  interfaces_menu (self.state is the same object)
- Fixed language_menu, settings_menu to use self.i18n shorthand
- Fixed all keyboard_manager references to use self.gui

…e(None) for back

- DeviceBar, WalletBar: rename self.parent -> self.gui (consistent with
  TitledScreen refactor); keep self.gui.show_menu() for forward navigation
  to specific menus (more readable at the call site than on_navigate)
- locked_menu, generate_seedphrase_menu: replace self.gui.show_menu(None)
  with self.on_navigate(None) — these are "go back" calls and should use
  the standard TitledScreen callback

…u to TitledScreen

Both classes are forms, not menus — they don't use get_menu_items() or
_build_menu_items() at all, only post_init(). Subclassing GenericMenu was
semantically misleading and added unnecessary indirection.

Changes:
- Inherit from TitledScreen instead of GenericMenu
- Replace TITLE_KEY + post_init(t, state) with a plain __init__(parent)
- Translate title via parent.i18n.t() before calling super().__init__()
- Set up body flex layout explicitly (was done implicitly by GenericMenu)
- Use t = self.i18n.t local alias for translations (self.state accessed directly)
- Drop unused imports: RED, ORANGE, GREEN