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>

scripts/bootstrap-ubuntu.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# Bootstrap an Ubuntu (24.04 "noble") NVIDIA-GPU VM to build/run the lumen Linux host
+# Bootstrap an Ubuntu (24.04 "noble") NVIDIA-GPU VM to build/run the punktfunk Linux host
 # and the M0 capture spike (headless Sway/wlroots -> PipeWire -> NVENC).
 #
 # Assumes the NVIDIA driver + an FFmpeg-with-NVENC are ALREADY installed (verify-only).
@@ -57,10 +57,10 @@ if have ffmpeg; then
         ok "FFmpeg has NVENC: $(ffmpeg -hide_banner -encoders 2>/dev/null | grep -oE '(hevc|h264)_nvenc' | paste -sd' ' -)"
         log "  smoke-test: 1s HEVC NVENC encode to null"
         if ffmpeg -hide_banner -loglevel error -f lavfi -i color=c=black:s=1280x720:d=1 \
-               -c:v hevc_nvenc -preset p1 -tune ull -f null - 2>/tmp/lumen_nvenc.err; then
+               -c:v hevc_nvenc -preset p1 -tune ull -f null - 2>/tmp/punktfunk_nvenc.err; then
             ok "hevc_nvenc encode succeeded — NVENC is usable in this guest"
         else
-            warn "hevc_nvenc encode FAILED (see /tmp/lumen_nvenc.err). Common cause on a VM: \
+            warn "hevc_nvenc encode FAILED (see /tmp/punktfunk_nvenc.err). Common cause on a VM: \
 missing libnvidia-encode.so.1 or an unlicensed vGPU."
         fi
     else