refactor(host/W6.1): extract the config() global into the pf-host-config leaf crate

Third de-coupling for the host crate carve (plan §W6.1 leaf). HostConfig + the config()
OnceLock (config.rs, pure std, zero deps) move to a new pf-host-config leaf so every
subsystem crate (pf-encode/pf-capture/pf-vdisplay/pf-gpu) can read process config WITHOUT
depending on the orchestrator. 34 crate::config::config() call sites across 19 files
repoint to pf_host_config::config(). thread_qos stays in the host for now (it calls
session_tuning::on_hot_thread — its own leaf-ification rides the encode carve).

Granular-crate decision (supersedes the plan's single pf-media): split capture/encode/
vdisplay into separate crates rather than one broad crate — the capture↔encode cycle is
broken by a shared frame-types leaf, and vdisplay→encode (can_open_another_session) is a
legal one-way edge since encode never references vdisplay.

Verified: Linux (home-worker-5) clippy -p pf-host-config -p punktfunk-host --all-targets
-D warnings; Windows (192.168.1.158) clippy --features nvenc,amf-qsv --all-targets green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/vdisplay/linux/gamescope.rs

@@ -1408,7 +1408,7 @@ fn spawn(w: u32, h: u32, hz: u32, cmd: Option<&str>, log: &std::path::Path) -> R
     let app = shape_dedicated_command(&app);
     let relay = ei_socket_file();
     let _ = std::fs::remove_file(&relay); // stale socket path from a previous session
-    let steam_mode = crate::config::config().gamescope_steam;
+    let steam_mode = pf_host_config::config().gamescope_steam;
     let mut cmd = Command::new("gamescope");
     add_bare_gamescope_args(&mut cmd, w, h, hz, steam_mode);
     cmd.args([

crates/punktfunk-host/src/vdisplay/session.rs

@@ -418,7 +418,7 @@ pub fn apply_session_env(_active: &ActiveSession) {}
 /// handshake error tell the client to simply retry.
 #[cfg(target_os = "linux")]
 pub fn try_recover_session() -> bool {
-    let Some(cmd) = crate::config::config().recover_session_cmd.clone() else {
+    let Some(cmd) = pf_host_config::config().recover_session_cmd.clone() else {
         return false;
     };
     static LAST_LAUNCH: std::sync::Mutex<Option<std::time::Instant>> = std::sync::Mutex::new(None);