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>

.gitea/workflows/ci.yml

@@ -1,4 +1,4 @@
-# CI for lumen (Gitea Actions, GitHub-Actions-compatible syntax).
+# CI for punktfunk (Gitea Actions, GitHub-Actions-compatible syntax).
 # Adjust `runs-on` to match your runner labels if not using the default ubuntu image.
 name: ci
 
@@ -34,10 +34,10 @@ jobs:
         run: cargo test --workspace --locked
 
       - name: C ABI harness (standalone link proof)
-        run: bash crates/lumen-core/tests/c/run.sh
+        run: bash crates/punktfunk-core/tests/c/run.sh
 
       - name: Verify generated header is committed & up to date
         run: |
-          cargo build -p lumen-core
-          git diff --exit-code include/lumen_core.h \
-            || (echo "include/lumen_core.h is stale — commit the regenerated header" && exit 1)
+          cargo build -p punktfunk-core
+          git diff --exit-code include/punktfunk_core.h \
+            || (echo "include/punktfunk_core.h is stale — commit the regenerated header" && exit 1)