feat(home-pages): make Map and Shutdown reorderable; v1.22 notes

The Map page had no Settings entry and Shutdown was pinned to the end of the
carousel because page_order held only 11 slots — full in the common
GPS+SENSORS config, so both pages fell back to being appended at nav time and
couldn't be moved. Grow page_order to 13 (== HPB_COUNT) so every page has a
reorderable slot, and add Map + Shutdown to the default order and the
required-append list.

To keep the persisted format backward-compatible (page_order sits mid-record,
not at the tail), the on-disk head stays the original 11 bytes at its existing
offset and the 2 new slots are appended at the file tail, matching the
append-only schema design. Bump SCHEMA_SENTINEL to 0xC0DE0019; on a pre-0x19
save the tail bytes are the old sentinel/EOF, so they're clamped to 0 and
ensurePageOrderInit re-appends Map/Shutdown into the freed slots on first use.

Drop the now-dead Shutdown-eviction path (13 slots fit all pages).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/companion_radio/NodePrefs.h

@@ -125,9 +125,11 @@ struct NodePrefs {  // persisted to file
   // Home screen page order: each byte = HomePageBit + 1. 0 terminates the list.
   // Validity gated by page_order_set magic (see below) — not by entry value range,
   // so a junk byte in 1..HPB_COUNT cannot trigger custom-order mode.
-  // (Array length = HPB_COUNT, declared as literal so the field offset is stable
-  // across builds that add new HomePageBit entries.)
-  uint8_t  page_order[11];
+  // Declared as a literal (not HPB_COUNT) so the field offset stays stable across
+  // builds that add HomePageBit entries. The first PAGE_ORDER_LEN_V1 bytes persist
+  // at this offset (backward-compatible); the remaining slots live at the file
+  // tail (see DataStore) so pre-0x0019 saves still load without shifting.
+  uint8_t  page_order[13];
   uint8_t  joystick_rotation;   // 0-3 steps CW; independent of display_rotation
   uint8_t  eink_full_refresh_every; // index into {0,5,10,20,30}: full refresh every N partials (0=off)
   uint8_t  page_order_set;      // 0xA5 = page_order is user-configured; anything else = use default
@@ -344,7 +346,7 @@ struct NodePrefs {  // persisted to file
   // adding/removing/reordering fields in DataStore::savePrefs/loadPrefsInt so
   // older saves are detected on load and skipped (zero-init defaults kept).
   // High 24 bits identify the file format; low byte is the schema revision.
-  static const uint32_t SCHEMA_SENTINEL = 0xC0DE0018;
+  static const uint32_t SCHEMA_SENTINEL = 0xC0DE0019;
 
   // Bit-index for each home page. Used by page_order (entries store bit+1) and
   // by home_pages_mask. Single source of truth — both HomeScreen::pageBit/bitToPage
@@ -366,10 +368,15 @@ struct NodePrefs {  // persisted to file
     HPB_COUNT      = 13,
   };
 
-  // Length of the persisted page_order[] array. Stable across firmware versions
-  // (don't grow without a schema migration). When HPB_COUNT exceeds this, extra
-  // visible pages are appended at navigation time via buildVisibleOrder fallback.
-  static const uint8_t PAGE_ORDER_LEN = 11;
+  // Number of usable page_order[] slots — one per home page (== HPB_COUNT), so
+  // every page can be reordered. Any page still missing from a saved order is
+  // appended at navigation time via buildVisibleOrder's fallback.
+  static const uint8_t PAGE_ORDER_LEN = 13;
+  // Bytes of page_order persisted at the original file offset. Slots beyond this
+  // (PAGE_ORDER_LEN - PAGE_ORDER_LEN_V1) are stored at the file tail, so a
+  // pre-0x0019 save — whose order was exactly this long — loads without shifting
+  // every field written after page_order.
+  static const uint8_t PAGE_ORDER_LEN_V1 = 11;
 
   // Bitmasks for home_pages_mask (bit=1 → page visible; 0 field = all visible).
   // SETTINGS and QUICK_MSG have no mask bit — they're always visible.