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/Sources/PunktfunkClient/PunktfunkClientApp.swift

@@ -0,0 +1,29 @@
+// PunktfunkClient — development app shell around PunktfunkKit (swift run PunktfunkClient).
+// Connect form → StreamView (AVSampleBufferDisplayLayer HEVC) + InputCapture.
+
+import AppKit
+import SwiftUI
+
+@main
+struct PunktfunkClientApp: App {
+    @NSApplicationDelegateAdaptor(AppDelegate.self) private var appDelegate
+
+    var body: some Scene {
+        WindowGroup("punktfunk") {
+            ContentView()
+        }
+    }
+}
+
+final class AppDelegate: NSObject, NSApplicationDelegate {
+    func applicationDidFinishLaunching(_ notification: Notification) {
+        // `swift run` launches an unbundled binary; promote it to a regular app so the
+        // window fronts and receives keyboard/mouse focus (GameController needs focus).
+        NSApp.setActivationPolicy(.regular)
+        NSApp.activate(ignoringOtherApps: true)
+    }
+
+    func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
+        true
+    }
+}