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/capture/linux/mod.rs

@@ -1626,7 +1626,7 @@ mod pipewire {
         // advertisement with every modifier its device samples from, so compositors that
         // never allocate LINEAR (Mutter+NVIDIA) still negotiate zero-copy dmabufs.
         #[cfg(feature = "pyrowave")]
-        if vaapi_passthrough && crate::config::config().encoder_pref.as_str() == "pyrowave" {
+        if vaapi_passthrough && pf_host_config::config().encoder_pref.as_str() == "pyrowave" {
             for m in crate::encode::pyrowave_capture_modifiers(
                 crate::zerocopy::drm_fourcc(PixelFormat::Bgrx).unwrap(),
             ) {

crates/punktfunk-host/src/capture/windows/idd_push.rs

@@ -1522,7 +1522,7 @@ impl Capturer for IddPushCapturer {
         // NVENC encodes N on the ASIC. We hand a rotating `OUT_RING` of output textures, so this is safe.
         // `PUNKTFUNK_IDD_DEPTH` overrides (1 disables pipelining; clamp to ≤ OUT_RING so a frame in flight
         // always has its own texture).
-        crate::config::config().idd_depth.clamp(1, OUT_RING)
+        pf_host_config::config().idd_depth.clamp(1, OUT_RING)
     }
 }