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>

crates/punktfunk-host/src/gamestream/mdns.rs

@@ -0,0 +1,37 @@
+//! mDNS advertisement of `_nvstream._tcp.local.` so Moonlight auto-discovers the host.
+//! (Manual "add host by IP" also works as a fallback, which is what we test with first.)
+
+use super::Host;
+use anyhow::{Context, Result};
+use mdns_sd::{ServiceDaemon, ServiceInfo};
+use std::collections::HashMap;
+
+/// Holds the mDNS daemon; dropping it unregisters the service.
+pub struct Advert {
+    _daemon: ServiceDaemon,
+}
+
+pub fn advertise(host: &Host) -> Result<Advert> {
+    let daemon = ServiceDaemon::new().context("create mDNS daemon")?;
+    let host_name = format!("{}.local.", host.hostname);
+    // No TXT records are required for Moonlight discovery; it resolves the A record and then
+    // GETs /serverinfo for capabilities.
+    let props: HashMap<String, String> = HashMap::new();
+    let service = ServiceInfo::new(
+        "_nvstream._tcp.local.",
+        &host.hostname,
+        &host_name,
+        host.local_ip,
+        host.http_port,
+        props,
+    )
+    .context("build mDNS ServiceInfo")?;
+    daemon.register(service).context("register mDNS service")?;
+    tracing::info!(
+        service = "_nvstream._tcp",
+        port = host.http_port,
+        host = %host_name,
+        "mDNS advertising"
+    );
+    Ok(Advert { _daemon: daemon })
+}