rename: lumen → punktfunk, everywhere

Full project rename, decided 2026-06-10:
- Crates/binaries: punktfunk-core / punktfunk-host / punktfunk-client-rs.
- C ABI: punktfunk_* symbols, Punktfunk* types, include/punktfunk_core.h,
  PUNKTFUNK_FEATURE_QUIC guard (header regenerated; cbindgen renames updated, incl.
  PUNKTFUNK_BTN_*/PUNKTFUNK_AXIS_* wire constants).
- Protocol: punktfunk/1 — control-plane magic LMN1 → PKF1, nonce salt lmn1 → pkf1.
  WIRE BREAK: clients must be rebuilt from this revision.
- Env knobs: PUNKTFUNK_VIDEO_SOURCE / PUNKTFUNK_COMPOSITOR / PUNKTFUNK_ZEROCOPY / ….
- Host config dir: ~/.config/punktfunk (the box's dir was migrated in place — the
  persistent identity is unchanged, pinned fingerprints stay valid).
- Swift package: PunktfunkKit + PunktfunkCore.xcframework + PunktfunkConnection
  (Sources/PunktfunkClient app + tests renamed with it); build-xcframework.sh updated.
- scripts/: 60-punktfunk.rules, punktfunk-host.service; OpenAPI doc regenerated.

Also: scripts/headless/run-headless-kde.sh — full headless Plasma bringup. Root cause of
"desktop but no apps/settings" over the stream: plasmashell launched without
XDG_MENU_PREFIX=plasma-, so the launcher resolved a nonexistent applications.menu and
rendered an empty menu. The script sets the complete KDE session env (menu prefix,
KDE_FULL_SESSION, session version) and rebuilds ksycoca before starting plasmashell.

Gate: 97/97 tests, clippy -D warnings (both feature sets), fmt, C-ABI harness PASS,
zero lumen references left outside .git.

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

crates/punktfunk-host/src/audio.rs

@@ -0,0 +1,36 @@
+//! Desktop audio capture for the GameStream audio stream. On Linux: a PipeWire stream that
+//! records the default sink's monitor (i.e. everything playing out of the system), delivered
+//! as interleaved `f32` stereo PCM at 48 kHz. The audio data plane (`gamestream::audio`)
+//! reframes this into fixed Opus frames, encodes, and sends it.
+
+use anyhow::Result;
+
+/// Opus/GameStream audio is 48 kHz stereo.
+pub const SAMPLE_RATE: u32 = 48_000;
+pub const CHANNELS: usize = 2;
+
+/// Produces interleaved `f32` stereo PCM (L,R,L,R,…) at [`SAMPLE_RATE`]. Lives on its own
+/// thread; never blocks the capture loop (drops if the consumer falls behind).
+pub trait AudioCapturer: Send {
+    /// Block until the next chunk of interleaved samples is available (variable size). The
+    /// caller reframes into fixed Opus frames.
+    fn next_chunk(&mut self) -> Result<Vec<f32>>;
+
+    /// Discard any buffered chunks (called when a persistent capturer is reused for a new
+    /// stream, so the client doesn't hear stale audio captured while idle). Default: no-op.
+    fn drain(&mut self) {}
+}
+
+/// Open a live capturer for the default sink monitor (system output) via PipeWire.
+#[cfg(target_os = "linux")]
+pub fn open_audio_capture() -> Result<Box<dyn AudioCapturer>> {
+    linux::PwAudioCapturer::open().map(|c| Box::new(c) as Box<dyn AudioCapturer>)
+}
+
+#[cfg(not(target_os = "linux"))]
+pub fn open_audio_capture() -> Result<Box<dyn AudioCapturer>> {
+    anyhow::bail!("audio capture requires Linux + PipeWire")
+}
+
+#[cfg(target_os = "linux")]
+mod linux;