refactor(companion): drop one-time prefs-migration cruft, fix stale Msg wake comments

loadPrefsInt()'s "sentinel mismatch" block had accumulated ~62 lines of
one-shot backfills tied to specific old NodePrefs::SCHEMA_SENTINEL values
(favourites/map home-page bits, split bot-command toggles, trail_units_idx,
bot_trigger_ch seed, scope mask/index zeroing). Reduce it to just the
sentinel read + mismatch log line -- an upgrade from a version old enough
to hit any of these now lands on today's plain defaults for that field
instead of a silently-seeded value, same outcome a fresh device already
gets. The ongoing per-field range clamps (defensive against any corrupt or
out-of-range byte, not version-specific) are untouched.

Same treatment for DataStore::loadScopeList()'s one-time synthesis of a
scope-list entry from the old single default_scope_name/key field: removed,
along with the scope_migrated_legacy plumbing in MyMesh::begin() that only
ran once that migration had just fired. loadScopeList() drops its now-
unused NodePrefs parameter and bool return.

Also trimmed ~25 per-field comments that over-specified which exact old
sentinel produced which stray byte, down to what the clamp actually
defends against -- except where the hex value explained a genuinely
non-obvious byte-aliasing interaction, which stays. One comment (scope
mask/index) was flagged and rewritten because it described the very
zeroing logic this change removes.

Drive-by: two comments still said Settings > Sound > "Msg wake" -- it's
been under Settings > Display for a while, per the enum's section grouping
in SettingsScreen.h.

Verified: sim_companion_radio and WioTrackerL1_companion_solo_dual build
clean, RAM/Flash usage unchanged (pure logic removal, no schema/layout
change).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

examples/companion_radio/main.cpp

@@ -497,7 +497,7 @@ extern "C" EMSCRIPTEN_KEEPALIVE int sim_test_disable_screen_timeout() {
 }
 
 // Sets NodePrefs::msg_wake_screen_off directly (the same field Settings >
-// Sound > "Msg wake" toggles -- SettingsScreen.h's MSG_WAKE item), so a test
+// Display > "Msg wake" toggles -- SettingsScreen.h's MSG_WAKE item), so a test
 // harness can verify UITask::newMsg()'s wake-gating without scripting the
 // on-device Settings accordion navigation key-by-key.
 extern "C" EMSCRIPTEN_KEEPALIVE int sim_test_set_msg_wake_disabled(int disabled) {