feat(ui-lvgl): 320x240 browser simulator, compose field fixes

Simulator: SIM_UI=lvgl variants/sim/build_wasm.sh builds ui-lvgl for the
browser. SimLcdDisplay blits LVGL's RGB565 flush to a 320x240 canvas and
LvglPort.h's sim branch feeds the mouse in as touch; LVGL comes from the
L2 env's libdeps, its objects cached in web/build/obj_lvgl/. web/lvgl.html
runs it beside a ui-new peer on a direct link, with a window.sim API for
headless checks. New hooks: sim_lcd_touch, sim_lcd_button,
sim_test_send_channel_msg.

Compose: the theme's padding left less than one line in the field, so it
scrolled vertically and text jumped; pad it to fit exactly one line. The
cursor is drawn only while FOCUSED, now set while the keyboard is up.
With the keyboard up the screen header hides so the conversation keeps a
message in view; the accent popup stays inside the keyboard, clear of the
field; channel bubbles put the age next to the sender (one line shorter);
the thread scrollbar shows only while scrolling.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

variants/sim/SimDisplayDriver.h

@@ -360,4 +360,88 @@ public:
   // (see the class comment) -- nothing left to flush.
   void endFrame() override { }
 };
+
+// 320x240 colour touch LCD for the ui-lvgl frontend (Wio Tracker L2 shape).
+// LVGL renders everything itself; this driver only owns the canvas and power
+// state. blit() takes an RGB565 area straight from LVGL's flush callback
+// (ui-lvgl/LvglPort.h) and putImageData()s it. The DisplayDriver text/shape
+// API is a no-op -- only main.cpp's "Loading..." splash calls it.
+//
+// Touch comes from the host page: sim_lcd_touch(x, y, down) on mouse/pointer
+// events, read back by LvglPort.h through touchState().
+class SimLcdDisplay : public DisplayDriver {
+  bool _on = false;
+public:
+  static const int W = 320, H = 240;
+  SimLcdDisplay() : DisplayDriver(W, H) { }
+
+  struct Touch { int x, y; bool down; };
+  static Touch& touchState() { static Touch t = {0, 0, false}; return t; }
+
+  bool begin() {
+    _on = true;
+    EM_ASM({
+      var tag = (typeof Module !== 'undefined' && Module['simInstanceTag']) ? Module['simInstanceTag'] : '';
+      var id = tag ? ('sim-canvas-' + tag) : 'sim-canvas';
+      var c = document.getElementById(id);
+      if (!c) { console.error('[sim] #' + id + ' not found in the host page'); return; }
+      Module.__simCtx = c.getContext('2d');
+      Module.__simCtx.fillStyle = '#000';
+      Module.__simCtx.fillRect(0, 0, $0, $1);
+    }, W, H);
+    return true;
+  }
+
+  // RGB565 (little-endian, as LVGL renders it) -> RGBA -> canvas.
+  void blit(int x, int y, int w, int h, const uint16_t* px) {
+    if (!_on) return;
+    EM_ASM({
+      if (!Module.__simCtx) return;
+      // (no bare commas: EM_ASM is a macro)
+      var src = $4 >> 1;
+      var n = $2 * $3;
+      var img = Module.__simCtx.createImageData($2, $3);
+      var d = img.data;
+      for (var i = 0; i < n; i++) {
+        var c = HEAPU16[src + i];
+        var r = (c >> 11) & 0x1F;
+        var g = (c >> 5) & 0x3F;
+        var b = c & 0x1F;
+        var o = i * 4;
+        d[o] = (r << 3) | (r >> 2);
+        d[o + 1] = (g << 2) | (g >> 4);
+        d[o + 2] = (b << 3) | (b >> 2);
+        d[o + 3] = 255;
+      }
+      Module.__simCtx.putImageData(img, $0, $1);
+    }, x, y, w, h, px);
+  }
+
+  bool isOn() override { return _on; }
+  void turnOn() override { _on = true; }
+  void turnOff() override {
+    _on = false;
+    EM_ASM({
+      if (!Module.__simCtx) return;
+      Module.__simCtx.fillStyle = '#000';
+      Module.__simCtx.fillRect(0, 0, $0, $1);
+    }, W, H);
+  }
+  void clear() override { }
+  void startFrame(Color bkg = DARK) override { (void)bkg; }
+  void setTextSize(int sz) override { (void)sz; }
+  void setColor(Color c) override { (void)c; }
+  void setCursor(int x, int y) override { (void)x; (void)y; }
+  void print(const char* str) override { (void)str; }
+  void fillRect(int x, int y, int w, int h) override { (void)x; (void)y; (void)w; (void)h; }
+  void drawRect(int x, int y, int w, int h) override { (void)x; (void)y; (void)w; (void)h; }
+  void drawXbm(int x, int y, const uint8_t* bits, int w, int h) override { (void)x; (void)y; (void)bits; (void)w; (void)h; }
+  uint16_t getTextWidth(const char* str) override { return str ? strlen(str) * 6 : 0; }
+  void endFrame() override { }
+};
+
+extern "C" EMSCRIPTEN_KEEPALIVE inline void sim_lcd_touch(int x, int y, int down) {
+  SimLcdDisplay::Touch& t = SimLcdDisplay::touchState();
+  t.x = x; t.y = y; t.down = down != 0;
+}
 #endif // __EMSCRIPTEN__