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/60-punktfunk.rules

@@ -0,0 +1,11 @@
+# udev rules for the punktfunk streaming host (mirrors Sunshine's 60-sunshine.rules).
+#
+# Grants the `input` group access to /dev/uinput so the host can create virtual gamepads
+# (one X-Box-360-class pad per connected Moonlight controller). `static_node` makes the node
+# exist before the uinput module loads.
+#
+# Install:
+#   sudo cp scripts/60-punktfunk.rules /etc/udev/rules.d/
+#   sudo usermod -aG input $USER       # then re-login (or reboot)
+#   sudo udevadm control --reload-rules && sudo udevadm trigger
+KERNEL=="uinput", SUBSYSTEM=="misc", OPTIONS+="static_node=uinput", GROUP="input", MODE="0660", TAG+="uaccess"