refactor(ui): apply code review fixes — bugs, risk, optimisations, cleanup

Fixes 7 bugs (timing UB on unsigned long, abs() no-op, XBM CRC PROGMEM
scan, CayenneLPP heap thrash ×2, UTF-8 reply prefix, lock-seq reset on
wake), 3 risk items (notif melody stop guard, bot trigger pre-lowercase,
lock-seq cleared on display wake), plus optimisations (fmtMsgAge/
getTextWidth caching, RTTTL builder consolidated to NodePrefs, HP_*
constants and homePageLabel table moved to NodePrefs, DataStore flat
lambda schema, translateUTF8Static factored out) and minor cleanup.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/helpers/ui/SH1106Display.cpp

@@ -50,6 +50,7 @@ void SH1106Display::startFrame(Color bkg)
 void SH1106Display::setTextSize(int sz)
 {
   _text_sz = sz;
+  _vw_dirty = true;
   display.setTextSize(sz);
 }