fix(ui): Favourites page polish + upgrade migration

Render issues:
- Drop the "FAVOURITES" title — it overlapped the node-name/battery top
  bar; the page-dots indicator already identifies the page
- Use the locally-computed content_y (matches other home pages) so tiles
  sit below the dots row instead of starting at headerH() + sepH()
- Add 2 px top/bottom margin inside the grid so cells don't hug the dots
  or the panel edge

Upgrade migration (visibility + position):
- Newly-loaded prefs with an older sentinel OR a non-default mask had
  HP_FAVOURITES off and could not be enabled — DataStore::loadPrefsInt
  now ORs HP_FAVOURITES into home_pages_mask whenever the sentinel
  doesn't match the current schema
- Existing page_order_set users were stuck because FAVOURITES wasn't in
  page_order, so movePageInOrder bailed — ensurePageOrderInit now
  detects the missing FAVOURITES entry and inserts it right after CLOCK,
  shifting the tail; if the array is already full the page still
  appears via the buildVisibleOrder fallback

Bug fix in ensurePageOrderInit verification loop: iterated to HPB_COUNT
(12) over a PAGE_ORDER_LEN (11) array → one OOB read per call. Now
bounded to PAGE_ORDER_LEN.

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

examples/companion_radio/DataStore.cpp

@@ -314,6 +314,12 @@ void DataStore::loadPrefsInt(const char *filename, NodePrefs& _prefs, double& no
   if (sentinel != NodePrefs::SCHEMA_SENTINEL) {
     MESH_DEBUG_PRINTLN("prefs schema sentinel mismatch: got 0x%08X, expected 0x%08X — re-saving on next change",
                        (unsigned)sentinel, (unsigned)NodePrefs::SCHEMA_SENTINEL);
+    // 0xC0DE0001 → 0xC0DE0002: FAVOURITES home page added. Older saves have it
+    // implicitly off (their mask doesn't include HP_FAVOURITES); turn it on so
+    // upgraded users see the new page by default and can toggle it later.
+    if (_prefs.home_pages_mask != 0) {
+      _prefs.home_pages_mask |= NodePrefs::HP_FAVOURITES;
+    }
   }
 
   file.close();