feat(android): mic uplink + connect-screen redesign

Microphone uplink (client → host's virtual mic, 0xCB) and a cleaner connect screen.

Mic (Rust-heavy, mirrors the audio playback path in reverse):
- crates/punktfunk-android/src/mic.rs: AAudio LowLatency **input** → realtime callback hands
  captured f32 to a channel → a worker thread Opus-encodes 20 ms stereo frames (48 kHz, VOIP,
  64 kbps) and calls NativeClient::send_mic. MicCapture owns the stream + encode thread (RAII stop).
- session.rs: SessionHandle gains a `mic` slot; nativeStartMic/nativeStopMic JNI (mirror of audio);
  stopped in Drop. NativeBridge: the two externs.
- Settings: a `micEnabled` flag + a Microphone toggle in SettingsScreen that requests RECORD_AUDIO
  (denied → stays off). StreamScreen starts the mic only if enabled AND the permission is held.

Connect-screen redesign:
- One scrollable Column (was a fixed centered layout that could clip with the new tab bar);
  host rows render via forEach (no nested LazyColumn). Colored section labels ("Saved hosts",
  "Discovered on the network", "Connect manually"), full-width host cards / fields / Connect button,
  a header + subtitle, and a muted footer.

Verified live (emulator pf_phone -> home-worker-2): toggling mic requests RECORD_AUDIO; with it
granted, a session sends mic frames (client "mic: sent=250 … peak=0.439" — real audio) and the host
logs "client datagram stream ended … mic=276". Redesigned screen confirmed via screenshots.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/android/kit/src/main/kotlin/io/unom/punktfunk/kit/NativeBridge.kt

@@ -84,6 +84,16 @@ object NativeBridge {
     /** Stop + join the audio thread and close AAudio, without closing the session. No-op on `0`. */
     external fun nativeStopAudio(handle: Long)
 
+    /**
+     * Start mic uplink: AAudio input → Opus (48 kHz stereo, 20 ms) → host (`send_mic` / 0xCB), all in
+     * Rust. No-op if already running. The caller MUST hold RECORD_AUDIO; otherwise the AAudio input
+     * stream fails to open and the rest of the session keeps streaming.
+     */
+    external fun nativeStartMic(handle: Long)
+
+    /** Stop + join the mic thread and close the AAudio input stream. No-op on `0`. */
+    external fun nativeStopMic(handle: Long)
+
     // ---- Input: Kotlin captures, Rust forwards to the host (send_input) ----
 
     /** Relative mouse move; dx/dy are device-pixel deltas (screen +y down). */