feat(ui): optional magnetic flip-cover screen lock via user-wired Hall sensor

No board in this repo has one built in, and no default pin is assumed
anywhere -- whoever wires a Hall-effect or reed sensor to a free GPIO sets
PIN_HALL_SENSOR (and HALL_ACTIVE_HIGH, for a sensor that pulls the pin high
rather than low on presence) as a build_flag on their own env. Entirely
opt-in and a no-op elsewhere, same pattern as PIN_GPIO1..4/ADC_MULTIPLIER/
CARDKB_ENABLE.

Level-triggered polling (like pollCardKB()) rather than an edge interrupt --
a magnet held near the sensor reads the same way every tick, so the new
pollHallSensor() only acts on the two transitions. Closing locks and blanks
the display with no wake grace (the cover is physically over the screen, so
there's nothing to show); opening unlocks and wakes it, with no key combo
either way. Both are independent of the Auto-lock setting, which is a
timeout, not a physical event.

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

release-notes.md

@@ -3,6 +3,7 @@
 ### What's new
 
 - **On-device community scope, and repeater-side scope filtering.** Settings › Radio gets a **Scope** field — type a region/community name (e.g. `pl`) and every device typing the same name derives the same shared tag, no key exchange needed; it's what your own DM/channel sends carry, previously only settable from a connected app. Tools › Repeater gains **Scope only** (only relay flood traffic matching your own scope, or one of the new **Extra scopes** below — a no-op until a scope is actually set, so it can't silently blackhole all forwarding) and **Extra scopes** (comma-separated additional regions to relay for, without changing what scope this device's own messages send under).
+- **Optional magnetic "flip cover" screen lock**, for anyone who wants to wire a Hall-effect or reed sensor to a free GPIO — no board ships one built in. Set `PIN_HALL_SENSOR` as a build flag on your own env and closing the cover locks and blanks the screen instantly, opening it unlocks and wakes it — no combo, independent of Auto-lock. See [Screen Lock](docs/solo_features/screen_lock/screen_lock.md#magnetic-cover-hall-sensor).
 
 ### Fixes