feat(ui): full e-ink refresh on screen change + prune gone favourites

Two UI quick wins from the 2026-07-05 review:

- E-ink: force a full (non-partial) refresh on the first frame of a new
  screen. Inter-screen ghosting was the most visible cheap win — the
  N-partials interval alone doesn't catch navigation. New
  DisplayDriver::forceFullRefresh() (no-op on OLED), set in setCurrScreen()
  and consumed by GxEPDDisplay::endFrame().

- Favourites: clear a stale "(gone)" tile at render time so it reverts to an
  empty "+" slot. Happens when prefs outlive the contact list (e.g. a wiped
  /contacts3); onContactRemoved only catches a live delete. Pruned slots are
  persisted once per pass (self-healing — an emptied slot can't re-fire).

Builds green: WioTrackerL1_companion_solo_dual (OLED),
WioTrackerL1Eink_companion_solo_dual (e-ink).

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

src/helpers/ui/DisplayDriver.h

@@ -272,6 +272,7 @@ public:
   virtual void setBrightness(uint8_t level) { }  // level 0-4 (min to max), no-op default
   virtual void setDisplayRotation(uint8_t rot) { }  // 0-3, no-op for fixed-orientation displays
   virtual void setFullRefreshInterval(uint8_t n) { }  // e-ink: do full refresh every n partial refreshes (0=never)
+  virtual void forceFullRefresh() { }  // e-ink: make the next frame a full (non-partial) refresh — clears ghosting on screen change; no-op on OLED
   virtual void endFrame() = 0;
 
 #ifdef ENABLE_SCREENSHOT

src/helpers/ui/GxEPDDisplay.cpp

@@ -275,10 +275,14 @@ void GxEPDDisplay::endFrame() {
   uint32_t crc = display_crc.finalize();
   if (crc != last_display_crc_value) {
     bool partial = true;
-    if (_full_refresh_interval > 0 && ++_partial_count >= _full_refresh_interval) {
+    // A forced full refresh (e.g. screen change) clears inter-screen ghosting.
+    // Short-circuit so _partial_count isn't bumped on the forced pass; the block
+    // resets it either way, matching the interval-driven full refresh.
+    if (_force_full || (_full_refresh_interval > 0 && ++_partial_count >= _full_refresh_interval)) {
       partial = false;
       _partial_count = 0;
     }
+    _force_full = false;
     display.display(partial);
     last_display_crc_value = crc;
   }

src/helpers/ui/GxEPDDisplay.h

@@ -64,6 +64,7 @@ class GxEPDDisplay : public DisplayDriver {
   int _text_sz = 1;
   uint8_t _full_refresh_interval = 0;
   uint8_t _partial_count = 0;
+  bool _force_full = false;   // set by forceFullRefresh(); consumed by the next endFrame()
 
   int16_t drawLemonChar(int16_t x, int16_t y, uint32_t cp, int sc);
   uint8_t lemonXAdvance(uint32_t cp, int sc);
@@ -144,5 +145,6 @@ public:
   }
   void setDisplayRotation(uint8_t rot) override;
   void setFullRefreshInterval(uint8_t n) override { _full_refresh_interval = n; _partial_count = 0; }
+  void forceFullRefresh() override { _force_full = true; }
   void endFrame() override;
 };