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>

clients/apple/test-loopback.sh

@@ -1,17 +1,17 @@
 #!/usr/bin/env bash
-# Loopback integration: a real lumen/1 host (synthetic source — pure protocol, runs fine on
+# Loopback integration: a real punktfunk/1 host (synthetic source — pure protocol, runs fine on
 # macOS) on 127.0.0.1, then the Swift integration tests against it through the xcframework.
 # The m3 host serves exactly one session and exits; the trap is just for failure paths.
 set -euo pipefail
 cd "$(dirname "$0")/../.."
 
-PORT="${LUMEN_LOOPBACK_PORT:-19778}"
+PORT="${PUNKTFUNK_LOOPBACK_PORT:-19778}"
 
-cargo build --release -p lumen-host
-target/release/lumen-host m3-host --port "$PORT" --source synthetic --frames 300 &
+cargo build --release -p punktfunk-host
+target/release/punktfunk-host m3-host --port "$PORT" --source synthetic --frames 300 &
 HOST_PID=$!
 trap 'kill "$HOST_PID" 2>/dev/null || true' EXIT
 sleep 1
 
 cd clients/apple
-LUMEN_LOOPBACK_PORT="$PORT" swift test --filter LoopbackIntegrationTests
+PUNKTFUNK_LOOPBACK_PORT="$PORT" swift test --filter LoopbackIntegrationTests