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/zerocopy/mod.rs

@@ -0,0 +1,50 @@
+//! Zero-copy capture→encode (plan §9): the PipeWire dmabuf is imported into CUDA via EGL and
+//! handed straight to NVENC, eliminating the per-frame CPU copies (at 5K the CPU-copy path
+//! moves ~3.5 GB/s). Opt in with `PUNKTFUNK_ZEROCOPY=1`; the CPU-copy path stays the default and
+//! the runtime fallback (foreign-allocator / no-dmabuf / import failure).
+//!
+//! Pieces: [`cuda`] (driver-API FFI + the shared `CUcontext` + device buffers), [`egl`] (the
+//! headless EGLDisplay + dmabuf→`EGLImage`→CUDA import). The encoder's CUDA-frame path lives in
+//! `encode/linux.rs`; the dmabuf negotiation lives in `capture/linux.rs`.
+
+pub mod cuda;
+pub mod egl;
+pub mod vulkan;
+
+pub use cuda::DeviceBuffer;
+pub use egl::{DmabufPlane, EglImporter};
+
+/// Whether the zero-copy path is opted in (`PUNKTFUNK_ZEROCOPY` truthy).
+pub fn enabled() -> bool {
+    std::env::var("PUNKTFUNK_ZEROCOPY")
+        .map(|v| matches!(v.trim(), "1" | "true" | "yes" | "on"))
+        .unwrap_or(false)
+}
+
+/// DRM FourCC for a packed 32-bit format name (little-endian, e.g. `b"XR24"`).
+const fn fourcc(c: &[u8; 4]) -> u32 {
+    (c[0] as u32) | ((c[1] as u32) << 8) | ((c[2] as u32) << 16) | ((c[3] as u32) << 24)
+}
+
+/// Map a SPA/our [`crate::capture::PixelFormat`] to the DRM FourCC EGL expects for import.
+/// SPA byte order `BGRx` ⇒ DRM `XRGB8888` (memory B,G,R,X), etc.
+pub fn drm_fourcc(format: crate::capture::PixelFormat) -> Option<u32> {
+    use crate::capture::PixelFormat::*;
+    Some(match format {
+        Bgrx => fourcc(b"XR24"), // DRM_FORMAT_XRGB8888
+        Bgra => fourcc(b"AR24"), // DRM_FORMAT_ARGB8888
+        Rgbx => fourcc(b"XB24"), // DRM_FORMAT_XBGR8888
+        Rgba => fourcc(b"AB24"), // DRM_FORMAT_ABGR8888
+        // 24-bit packed RGB/BGR have no straightforward dmabuf import here; use the CPU path.
+        Rgb | Bgr => return None,
+    })
+}
+
+/// Standalone probe (the `zerocopy-probe` subcommand): initialize the EGL importer + CUDA
+/// context and report. De-risks the FFI/linking/GPU-access without needing a capture session.
+pub fn probe() -> anyhow::Result<()> {
+    let _importer = EglImporter::new()?;
+    let ctx = cuda::context()?;
+    tracing::info!(cuda_ctx = ?ctx, "zero-copy probe OK — EGL display + CUDA context initialized");
+    Ok(())
+}