fix(sim): text-width/render bugs, splash version, wasm-fetch error, battery lag

Code-review pass over the buzzer/sim commits turned up several real bugs,
plus two issues found afterward from manual browser testing:

Rendering (SimDisplayDriverCanvas, variants/sim/SimDisplayDriver.h + target.cpp):
- getTextWidth() measured UTF-8 BYTES (strlen()*6), not codepoints. Since
  b067e95b stopped stripping accents, any accented string now measures
  double its real width -- mis-centred titles, premature ellipsis/marquee,
  badges pushed off-screen. Now uses the real MiscFixedRenderer measurement
  (miscFixedTextWidth()), same as SH1106Display/SSD1306Display.
- Added the matching getCodepointWidth() override (O(1) single-glyph
  advance), same pattern as SSD1306Display.
- isSingleFont() was left at the base class's `false`, though this backend
  only ever renders MiscFixed -- UITask.cpp's status-bar indicator height
  keys off this (`lh-2` vs `lh`), so the sim drew it 2px taller than a real
  board.
- print() blitted the full 128x64 canvas on every call (dozens per frame,
  60fps) -- now tracks a dirty bounding box and only clears/blits the
  region actually touched.

Web Audio (buzzer bridge, index.html + mesh.html):
- No AudioContext.resume() -- a context created (or later suspended) in the
  'suspended' state (Safari/Firefox, or any browser backgrounding the tab)
  stayed silent forever. Now resumed on every gesture.
- linearRampToValueAtTime with no anchoring setValueAtTime interpolates
  from the LAST scheduled event, not "now" -- so the anti-click ramps could
  effectively snap instead of fading. Fixed with cancelScheduledValues +
  setValueAtTime(current) before each ramp.
- mesh.html: a gesture only armed the clicked instance's audio. Click A,
  send A->B, and B (the one actually meant to beep on receipt) stayed
  silent. Now any gesture arms both A and B.
- RTTTL rests (freq=0, still "playing") now explicitly hold pitch and drop
  gain instead of it happening to work by coincidence.

Misc: sim_test_get_num_contacts() was missing the g_sim_ready gate every
other sim_test_* hook has, so it could return a bogus negative count before
setup() finishes seeding num_contacts.

Splash screen missing "Solo <version>" bar: variants/sim never defined
FIRMWARE_SOLO_BUILD (every real Solo board does), so SplashScreen silently
skipped that whole line -- the sim looked like a plain non-Solo companion
build. Added -D FIRMWARE_SOLO_BUILD=1 to platformio.ini and build_wasm.sh.
Verified on a real canvas screenshot: "MESHCORE 1.17.1 / 19 Aug 2026 /
Solo v1.27".

Wasm-fetch error message: "failed to start: RuntimeError: Aborted(both
async and sync fetching of the wasm failed)" is Emscripten's own opaque
message for the single most common real cause -- the page opened via
file://...index.html instead of served over http(s) (fetch() on a local
file is blocked by CORS in both Chrome and Safari, confirmed by reproducing
the exact same error/stack via file://). Both harnesses now detect
location.protocol === 'file:' and show an actionable message with the
one-line fix instead of the raw stack trace.

Battery-set latency: SimMainBoard's battery value is an exact, instantaneous
JS-set integer (see sim_battery_set_mv()), but UITask's battery-check code
polls it every 8s and runs it through an EMA (alpha=0.2) meant to smooth a
REAL board's noisy ADC -- so a value typed into the demo UI could take tens
of seconds to visibly settle. SIM_PLATFORM now checks every 250ms and skips
the EMA (nothing to smooth), since the reading is already clean. Measured
on real canvas pixels: indicator update now lands within one screen-refresh
cycle instead of up to 8s+.

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

variants/sim/platformio.ini

@@ -33,6 +33,12 @@ build_flags =
   ; way). genericBuzzer's own #ifdef SIM_PLATFORM branch (src/helpers/ui/
   ; buzzer.cpp) never touches a real pin, so the value itself is unused.
   -D PIN_BUZZER=0
+  ; Every real board running this same ui-new/ tree builds as a Solo config
+  ; (see e.g. solo/heltec_v3/platformio.ini) -- without this, SplashScreen
+  ; (UITask.cpp) skips the whole "Solo <version>" bar under the big MeshCore
+  ; version digits, and the splash silently looks like a plain non-Solo
+  ; companion build instead of what it actually is.
+  -D FIRMWARE_SOLO_BUILD=1
   -D MAX_CONTACTS=100
   -D MAX_GROUP_CHANNELS=8
   -I variants/sim/arduino