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/native/handshake.rs

@@ -207,7 +207,7 @@ pub(super) async fn negotiate(
     // Welcome, exactly like the 4:4:4 gate below, so `color` reflects what we'll really emit —
     // the honest-downgrade channel: a GPU/backend that can't 10-bit yields 8-bit AND an SDR
     // label that matches the stream.
-    let host_wants_10bit = crate::config::config().ten_bit;
+    let host_wants_10bit = pf_host_config::config().ten_bit;
     let client_supports_10bit = hello.video_caps & punktfunk_core::quic::VIDEO_CAP_10BIT != 0;
     // The GPU probe may open a tiny encoder on first use, so run it off the reactor like the
     // 4:4:4 probe below (blocking probes → spawn_blocking), short-circuited behind the cheap
@@ -239,7 +239,7 @@ pub(super) async fn negotiate(
     // what we'll really emit — the honest-downgrade channel: if any gate fails the client is
     // told 4:2:0 before it builds its decoder. The probe opens a tiny encoder; it runs only
     // when the earlier gates pass and is cached after the first.
-    let host_wants_444 = crate::config::config().four_four_four;
+    let host_wants_444 = pf_host_config::config().four_four_four;
     let client_supports_444 = hello.video_caps & punktfunk_core::quic::VIDEO_CAP_444 != 0;
     // The active capturer must be able to deliver a full-chroma (RGB) source — the honest-downgrade
     // gate. Linux's portal capturer can; the Windows IDD-push path delivers subsampled NV12/P010