feat(ui): Favourites home page (phase 1: storage + read-only grid)

New home page rendering 6 pinned-contact slots. Grid transposes to
orientation: landscape → 3×2, portrait → 2×3. Joystick claims UP/DOWN
and inner LEFT/RIGHT for grid nav; edge LEFT/RIGHT fall through to
page navigation. Selected tile inverts via drawSelectionRow, filled
tile shows contact name + unread badge, empty tile shows "+".

Storage:
- NodePrefs::favourite_contacts[6][6] (6-byte pub_key prefix per slot,
  all-zero = empty; collision probability with a real key is 2^-48)
- HomePageBit gains HPB_FAVOURITES = 11 (HPB_COUNT = 12), with a new
  HP_FAVOURITES mask bit so the page is toggleable in Settings
- New PAGE_ORDER_LEN constant decouples the persisted array length (11)
  from the page-type count; loops over page_order now use it, value-range
  checks still use HPB_COUNT
- homePageBit returns 0 for HPB_SETTINGS / HPB_QUICK_MSG explicitly
  rather than by bit-index range, so HPB_FAVOURITES (bit 11) is correctly
  treated as toggleable
- Default order inserts FAVOURITES after CLOCK; SHUTDOWN drops to the
  fallback "missing pages" append (still reachable, lands at end)

Schema sentinel bumped to 0xC0DE0002. DataStore::loadPrefsInt and
savePrefs read/write the new field. Older saves leave the field
zero-initialised (all slots empty), which is the natural starting state.

Phase 2 (Pin from Contact options) and Phase 3 (Pin from empty-slot
mini picker) wire interactions; this commit handles render + nav only.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/companion_radio/ui-new/UITask.h

@@ -138,6 +138,7 @@ public:
   }
   void clearAllDMUnread() { memset(_dm_unread_table, 0, sizeof(_dm_unread_table)); }
   bool hasDisplay() const { return _display != NULL; }
+  DisplayDriver* getDisplay() const { return _display; }
   bool isButtonPressed() const;
 
   bool isBuzzerQuiet() {