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/apps.rs

@@ -0,0 +1,143 @@
+//! The app catalog: what `/applist` advertises and what `/launch?appid=N` selects. Each entry
+//! maps to a session recipe — which compositor backend hosts it and (for gamescope) which
+//! command runs nested. Loaded from `~/.config/punktfunk/apps.json`; sensible defaults otherwise.
+//!
+//! ```json
+//! [ {"id":1,"title":"Desktop"},
+//!   {"id":2,"title":"Steam","compositor":"gamescope","cmd":"steam -gamepadui"} ]
+//! ```
+
+use serde_json::Value;
+
+#[derive(Clone, Debug)]
+pub struct AppEntry {
+    pub id: u32,
+    pub title: String,
+    /// `None` = auto-detect (the desktop session's compositor).
+    pub compositor: Option<crate::vdisplay::Compositor>,
+    /// Command gamescope runs nested (gamescope entries only).
+    pub cmd: Option<String>,
+}
+
+fn config_path() -> Option<std::path::PathBuf> {
+    Some(std::path::Path::new(&std::env::var("HOME").ok()?).join(".config/punktfunk/apps.json"))
+}
+
+fn parse_compositor(s: &str) -> Option<crate::vdisplay::Compositor> {
+    use crate::vdisplay::Compositor::*;
+    match s.to_ascii_lowercase().as_str() {
+        "kwin" | "kde" => Some(Kwin),
+        "mutter" | "gnome" => Some(Mutter),
+        "gamescope" => Some(Gamescope),
+        "wlroots" | "sway" => Some(Wlroots),
+        _ => None,
+    }
+}
+
+/// The catalog: the user's `apps.json` if present, else defaults (Desktop, plus gamescope
+/// entries when gamescope is installed).
+pub fn catalog() -> Vec<AppEntry> {
+    if let Some(path) = config_path() {
+        if let Ok(raw) = std::fs::read_to_string(&path) {
+            match serde_json::from_str::<Value>(&raw) {
+                Ok(Value::Array(items)) => {
+                    let apps: Vec<AppEntry> = items
+                        .iter()
+                        .filter_map(|it| {
+                            Some(AppEntry {
+                                id: it.get("id")?.as_u64()? as u32,
+                                title: it.get("title")?.as_str()?.to_string(),
+                                compositor: it
+                                    .get("compositor")
+                                    .and_then(|c| c.as_str())
+                                    .and_then(parse_compositor),
+                                cmd: it.get("cmd").and_then(|c| c.as_str()).map(String::from),
+                            })
+                        })
+                        .collect();
+                    if !apps.is_empty() {
+                        return apps;
+                    }
+                    tracing::warn!(path = %path.display(), "apps.json parsed to zero entries — using defaults");
+                }
+                _ => {
+                    tracing::warn!(path = %path.display(), "apps.json malformed — using defaults")
+                }
+            }
+        }
+    }
+    let mut apps = vec![AppEntry {
+        id: 1,
+        title: "Desktop".into(),
+        compositor: None,
+        cmd: None,
+    }];
+    if which("gamescope") {
+        if which("steam") {
+            apps.push(AppEntry {
+                id: 2,
+                title: "Steam".into(),
+                compositor: Some(crate::vdisplay::Compositor::Gamescope),
+                cmd: Some("steam -gamepadui".into()),
+            });
+        }
+        if which("vkcube") {
+            apps.push(AppEntry {
+                id: 3,
+                title: "vkcube (test)".into(),
+                compositor: Some(crate::vdisplay::Compositor::Gamescope),
+                cmd: Some("vkcube".into()),
+            });
+        }
+    }
+    apps
+}
+
+pub fn by_id(id: u32) -> Option<AppEntry> {
+    catalog().into_iter().find(|a| a.id == id)
+}
+
+/// Render the GameStream `/applist` XML.
+pub fn applist_xml() -> String {
+    let mut xml =
+        String::from("<?xml version=\"1.0\" encoding=\"utf-8\"?>\n<root status_code=\"200\">\n");
+    for app in catalog() {
+        xml.push_str(&format!(
+            "<App>\n<IsHdrSupported>0</IsHdrSupported>\n<AppTitle>{}</AppTitle>\n<ID>{}</ID>\n</App>\n",
+            xml_escape(&app.title),
+            app.id
+        ));
+    }
+    xml.push_str("</root>\n");
+    xml
+}
+
+fn xml_escape(s: &str) -> String {
+    s.replace('&', "&amp;")
+        .replace('<', "&lt;")
+        .replace('>', "&gt;")
+}
+
+fn which(bin: &str) -> bool {
+    std::env::var_os("PATH")
+        .is_some_and(|paths| std::env::split_paths(&paths).any(|d| d.join(bin).is_file()))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn default_catalog_has_desktop() {
+        let apps = catalog();
+        assert!(apps.iter().any(|a| a.id == 1 && a.title == "Desktop"));
+    }
+
+    #[test]
+    fn applist_xml_is_wellformed_ish() {
+        let xml = applist_xml();
+        assert!(xml.contains("<AppTitle>Desktop</AppTitle>"));
+        assert!(xml.starts_with("<?xml"));
+        assert_eq!(xml.matches("<App>").count(), xml.matches("</App>").count());
+    }
+}