feat(core+host+android): committed-text input plane (IME path) — InputKind::TextInput

The VK key-event vocabulary cannot express text an input method COMMITS
(autocorrect, gesture typing, non-Latin scripts, emoji). Add a first-class
text event and negotiate it:

- punktfunk-core: InputKind::TextInput (= 15) carries one Unicode scalar per
  event in `code`; HOST_CAP_TEXT_INPUT (0x04) in Welcome::host_caps.
- Host advertises the cap only where the session's inject backend can type
  text: Windows SendInput (KEYEVENTF_UNICODE, surrogate-pair aware) and the
  Linux wlroots backend — a dedicated second zwp_virtual_keyboard whose xkb
  keymap grows Unicode keysyms on demand (the wtype model), so keymap
  re-uploads never disturb the main device's layout/modifier state. The
  KWin-fake-input/libei/gamescope backends can only press layout keycodes, so
  those sessions don't set the bit and clients keep the VK fallback.
- GameStream plane: Moonlight's UTF-8 text packet (MAGIC_UTF8, previously
  recognized-and-dropped) now decodes to the same TextInput events.
- Android: KeyCaptureView picks a real editable InputConnection when the host
  has the cap — the IME runs its full machinery, mirrored to the host live via
  common-prefix diffs of the composition (backspaces + new suffix), with
  setComposingRegion adopting committed text so autocorrect-revert flows diff
  instead of retyping; newline→Enter, deleteSurroundingText→Backspace/Delete.
  Older hosts keep the TYPE_NULL raw-key path unchanged.
- keymap: media VKs (0xB0-0xB3) → evdev so the Android media keys land on
  Linux hosts too.

Verified: punktfunk-core + host gamestream + pf-inject tests green on Linux
(Ubuntu box), clippy clean; Android app+native builds.

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

crates/pf-inject/src/inject/keymap.rs

@@ -36,6 +36,12 @@ pub fn vk_to_evdev(vk: u8) -> Option<u16> {
         0x2D => Some(110), // VK_INSERT   -> KEY_INSERT
         0x2E => Some(111), // VK_DELETE   -> KEY_DELETE
 
+        // --- Consumer/media keys (Android TV remotes, keyboard media rows) ---
+        0xB0 => Some(163), // VK_MEDIA_NEXT_TRACK -> KEY_NEXTSONG
+        0xB1 => Some(165), // VK_MEDIA_PREV_TRACK -> KEY_PREVIOUSSONG
+        0xB2 => Some(166), // VK_MEDIA_STOP       -> KEY_STOPCD
+        0xB3 => Some(164), // VK_MEDIA_PLAY_PAUSE -> KEY_PLAYPAUSE
+
         // --- Generic modifiers ---
         0x10 => Some(42), // VK_SHIFT   -> KEY_LEFTSHIFT
         0x11 => Some(29), // VK_CONTROL -> KEY_LEFTCTRL