feat(companion): contact expiry + prune, and scope-list follow-up fixes

Settings > Contacts gains "Expire" (Off/7d/30d/90d) and a "Prune now" action
that counts first and asks before removing anything. A contact with no
advert/update within the threshold is eligible; favourites are always kept.
Thresholds and their labels live in one NodePrefs table so the age shown and
the age enforced can't drift. SCHEMA_SENTINEL -> 0xC0DE002C (sizeof unchanged
at 2824, confirmed on native and a real WioTrackerL1 build).

Also fixes four bugs in the scope list from 89c02eea:

- removeScope() saved /scopes1 but never savePrefs(), so the ch_scope_idx[]
  and repeat_extra_scope_mask fix-ups it makes were lost on reboot, leaving
  shifted entries against unshifted indices.
- CMD_SET_DEFAULT_FLOOD_SCOPE wrote the legacy fields directly instead of
  going through setPrimaryScope(), so the app's default-scope setting had
  nothing reading it once sends resolved through the list.
- The reverse direction was stale too: an on-device "Set as default" never
  refreshed default_scope_name/key, so CMD_GET_DEFAULT_FLOOD_SCOPE reported
  a scope the device had stopped using. New syncLegacyDefaultScope().
- Upgrading from the old single Scope field set the default (so DMs kept it)
  but left every channel unscoped, since "*" means unscoped, not "inherit".
  loadScopeList() now reports when it migrated and begin() seeds the channels
  that already exist, leaving empty slots alone.

"Set default" -> "Set as default", and setting it now says what it governs
("Default: DMs + relay") rather than leaving the [default] marker to imply
more than it does.

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

release-notes.md

@@ -4,7 +4,8 @@
 
 - **The Clock/Lock dashboard gets a separate "Altitude (GPS)" field**, alongside the existing barometric one (now labelled "Altitude (Baro)") — the original single Altitude field only ever read a barometric sensor's telemetry, showing `--` on any board without one even with a perfectly good GPS fix.
 - **Received messages now show how many hops they actually took to reach you**, right in the message list — the same tiny digit-icon a sent message already uses for its repeater/echo count, now shown for incoming DMs and channel posts too, using the hop path the mesh already records for them.
-- **Scope is now a shared, freely-definable list, not one device-wide text field.** Settings › Radio › Scope manages a small named list (`*`/wildcard always first, plus a movable default) instead of a single free-typed name. Each channel picks exactly one scope of its own — a `Scope: <name>` row in the channel's context menu, matching the phone app's own per-channel region picker — and the channel's history title shows the tag when it's set to anything but `*`. Tools › Repeater's "Extra scopes" now multi-selects from the same list instead of comma-typing region names, capped at the same 4 active relay scopes as before. DMs and any not-yet-assigned channel keep using the list's current default, so an existing single-scope setup carries over unchanged on upgrade.
+- **Scope is now a shared, freely-definable list, not one device-wide text field.** Settings › Radio › Scope manages a small named list (`*`/wildcard always first, plus a movable default) instead of a single free-typed name. Each channel picks exactly one scope of its own — a `Scope: <name>` row in the channel's context menu, matching the phone app's own per-channel region picker — and the channel's history title shows the tag when it's set to anything but `*`. Tools › Repeater's "Extra scopes" now multi-selects from the same list instead of comma-typing region names, capped at the same 4 active relay scopes as before. A channel set to `*` sends unscoped; DMs and the repeater's primary relay slot follow the list's default entry. Upgrading carries an existing single-scope setup over unchanged: the old Scope becomes the default entry and every channel you already had is seeded with it, so nothing changes on the air.
+- **Settings › Contacts can now clean out contacts you haven't heard from in a while.** New "Expire" option (Off/7d/30d/90d) plus a "Prune now" action that shows exactly how many contacts would be removed before you confirm. Favourites are always kept regardless of age.
 
 ### Fixes