feat(sim): board feature parity (reset/GPS/sensors/admin/keyboard) + input fixes

Rounds out the browser sim harness with the rest of the physical board's
interactions: a reset button (JS-driven, since board.reboot() is inert
under -sEXIT_RUNTIME=0), GPS input wired into a real LocationProvider via
new SimSensorManager, JS-settable battery/environment telemetry, an
admin/repeater-login test hook (sendRoomLogin against the default
"password"), and full physical-keyboard text entry (printable ASCII
passthrough into the existing KeyboardWidget, Tab->KEY_KB_ENTER submit).

Also fixes three real bugs found while exercising all of this in a real
browser:
- UITask.cpp's native-only stdin poll branch had no __EMSCRIPTEN__
  exclusion, so it also compiled into the wasm build and called a real,
  blocking window.prompt() on nearly every frame -- the actual cause of
  the reported time/controls jumping. Now gated to native only.
- 'n'/'p' were mapped as Next/Prev keyboard shortcuts, colliding with
  typing those literal letters. Removed the shortcuts; added explicit
  Next/Prev buttons to mesh.html (previously relied solely on them).
- Buttons grabbed native browser keyboard focus on click, so a later
  stray Enter/Space could silently re-trigger a previously-clicked button
  (e.g. Reset). mousedown now calls preventDefault() on all buttons.

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

examples/companion_radio/ui-new/UITask.cpp

@@ -2424,7 +2424,21 @@ void UITask::loop() {
   } else if (ev == BUTTON_EVENT_TRIPLE_CLICK) {
     if (!_locked) enqueueKey(handleTripleClick(KEY_SELECT));
   }
-#elif defined(SIM_PLATFORM)
+#elif defined(SIM_PLATFORM) && !defined(__EMSCRIPTEN__)
+  // Native terminal input ONLY -- this branch previously had no
+  // __EMSCRIPTEN__ exclusion, so it also compiled into the wasm build
+  // (SIM_PLATFORM is defined there too, and UI_HAS_JOYSTICK/PIN_USER_BTN
+  // are both unset for variants/sim). Every tick it called real select()/
+  // read() on fd 0; under Emscripten, with no stdin ever wired up, that
+  // hits the runtime's default TTY device, which falls back to a real,
+  // blocking window.prompt("Input: ") -- so every single browser tab
+  // running the wasm build was popping a native dialog on nearly every
+  // frame, discovered by seeing Playwright's page 'dialog' event fire
+  // continuously from the moment the module boots. The wasm build's own
+  // input already comes through sim_enqueue_key()/injectSimKey() (see
+  // above, in the #if defined(SIM_PLATFORM) && defined(__EMSCRIPTEN__)
+  // block) -- this stdin-poll branch was only ever meant for Phase 1's
+  // native terminal target.
   // Native terminal input: stdin is put into raw/non-canonical mode by
   // variants/sim/sim_main.cpp's main(), so keys arrive here one at a time
   // with no Enter-to-submit line buffering. Non-blocking select() on fd 0