Remove Controller screen, global button shortcuts, touch-toggled splash

UX overhaul:
- Drop the Controller screen entirely (touch zones, swipe gestures, HID
  gesture engine, four icon arrays, hand icon)
- Two persistent screens (Usage, Bluetooth) cycled by the middle PWR
  button; splash becomes a touch-toggled welcome animation
- Left button (GPIO 0): hold to send Space (Claude Code voice-mode PTT)
- Right button (GPIO 18): press to send Shift+Tab (mode toggle)
- Middle button on splash cycles animations instead of screens
- Remove USB plug/unplug auto-switch (Controller was the unplug target)
- Hide battery indicator on splash when in LOW state — it's noisy over
  the pixel-art animations

Implementation:
- Delete firmware/src/hid.{cpp,h} and touch.{cpp,h}; their roles fold
  into main.cpp button handlers and LVGL CLICKED events respectively
- splash_get_root() exposes the splash container so ui.cpp can attach
  a click handler for the dismiss-on-tap behavior
- Tap detection uses LVGL's built-in LV_EVENT_CLICKED with event
  bubbling on the inner panels — debouncing is handled by LVGL
- On Bluetooth screen, only the Reset Bluetooth zone is clickable;
  taps elsewhere are no-ops (no conflict with splash toggle)

Docs:
- README: drop Controller from screens table, rewrite Physical buttons
  table, remove Gesture controls section
- CLAUDE.md: update file map, button assignments, drop gesture refs

firmware/src/splash.h

@@ -22,6 +22,9 @@ void splash_set_active(bool active);
 void splash_show(void);
 void splash_hide(void);
 
+// Root container (so ui.cpp can attach a click event).
+lv_obj_t* splash_get_root(void);
+
 // Current animation name (for debug/UI).
 const char *splash_current_name(void);