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/run-headless-kde.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+# Headless KDE Plasma session for the punktfunk host (no KMS scanout → kwin --virtual).
+#
+# Brings up the full desktop, not just the compositor. The env matters: without
+# XDG_MENU_PREFIX=plasma- the launcher resolves ${XDG_MENU_PREFIX}applications.menu →
+# "applications.menu", which doesn't exist on KDE installs (it ships
+# plasma-applications.menu) — plasmashell runs fine but the menu shows NO applications
+# and no System Settings entry. kded6/krunner/kglobalacceld are D-Bus-activated once
+# plasmashell starts in the right session env.
+#
+#   bash scripts/headless/run-headless-kde.sh [WxH]    # default 1920x1080
+#
+# Then in another shell:
+#   WAYLAND_DISPLAY=wayland-kde XDG_CURRENT_DESKTOP=KDE PUNKTFUNK_ZEROCOPY=1 \
+#     punktfunk-host m3-host --source virtual --seconds 14400
+set -euo pipefail
+
+RES="${1:-1920x1080}"
+W="${RES%x*}"
+H="${RES#*x}"
+
+export XDG_RUNTIME_DIR="${XDG_RUNTIME_DIR:-/run/user/$(id -u)}"
+export DBUS_SESSION_BUS_ADDRESS="${DBUS_SESSION_BUS_ADDRESS:-unix:path=$XDG_RUNTIME_DIR/bus}"
+export XDG_CURRENT_DESKTOP=KDE
+export XDG_MENU_PREFIX=plasma-
+export KDE_FULL_SESSION=true
+export KDE_SESSION_VERSION=6
+export DESKTOP_SESSION=plasma
+export WAYLAND_DISPLAY=wayland-kde
+export KWIN_WAYLAND_NO_PERMISSION_CHECKS=1
+
+kwin_wayland --virtual --width "$W" --height "$H" --no-lockscreen \
+    --socket "$WAYLAND_DISPLAY" &
+KWIN_PID=$!
+sleep 2
+
+kbuildsycoca6 >/dev/null 2>&1 || true # rebuild the menu cache under the correct env
+plasmashell &
+
+echo "headless KDE up on $WAYLAND_DISPLAY ($RES), kwin pid $KWIN_PID"
+wait "$KWIN_PID"