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/headless/prepare-session.sh

@@ -2,8 +2,8 @@
 # Run AFTER headless Sway is up (run-headless-sway.sh), from a second shell on the same
 # user. It: (1) points this shell at the running Sway, (2) gives HEADLESS-1 a real refresh
 # clock (an idle/0 mHz output produces no frames), (3) imports the env the ScreenCast portal
-# needs to find Sway and pick the wlr backend, and (4) writes /tmp/lumen-sway-env.sh so
-# other shells (e.g. `cargo run -p lumen-host`) can `source` it.
+# needs to find Sway and pick the wlr backend, and (4) writes /tmp/punktfunk-sway-env.sh so
+# other shells (e.g. `cargo run -p punktfunk-host`) can `source` it.
 #
 # Usage: bash scripts/headless/prepare-session.sh [WxH@RHz]   (default 1920x1080@60Hz)
 set -euo pipefail
@@ -32,7 +32,7 @@ echo "HEADLESS-1 set to $MODE"
 systemctl --user import-environment WAYLAND_DISPLAY XDG_CURRENT_DESKTOP SWAYSOCK XDG_RUNTIME_DIR 2>/dev/null || true
 dbus-update-activation-environment --systemd WAYLAND_DISPLAY XDG_CURRENT_DESKTOP SWAYSOCK 2>/dev/null || true
 
-cat > /tmp/lumen-sway-env.sh <<EOF
+cat > /tmp/punktfunk-sway-env.sh <<EOF
 export XDG_RUNTIME_DIR=$XDG_RUNTIME_DIR
 export WAYLAND_DISPLAY=$WAYLAND_DISPLAY
 export XDG_CURRENT_DESKTOP=sway
@@ -42,8 +42,8 @@ EOF
 
 cat <<EOF
 session ready. From any shell on this user:
-    source /tmp/lumen-sway-env.sh
+    source /tmp/punktfunk-sway-env.sh
     swaymsg exec foot          # optional: animated on-screen content
-    cargo run -p lumen-host -- m0 --source portal --seconds 5 --out /tmp/lumen-m0.h265
-    ffprobe /tmp/lumen-m0.h265
+    cargo run -p punktfunk-host -- m0 --source portal --seconds 5 --out /tmp/punktfunk-m0.h265
+    ffprobe /tmp/punktfunk-m0.h265
 EOF