refactor(client): extract UI-agnostic plumbing into pf-client-core (phase 0)

Session pump, FFmpeg decode, PipeWire audio, SDL3 gamepads, keymap, trust
store, mDNS discovery, library client and Wake-on-LAN move verbatim from
clients/linux into crates/pf-client-core, shared with the upcoming Vulkan
session binary (punktfunk-planning: linux-client-rearchitecture.md).
The GTK client re-exports them at the crate root so every existing
crate::-path keeps resolving; its manifest drops the moved-only deps.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/linux/README.md

@@ -78,15 +78,15 @@ src/
   ui_trust.rs             TOFU / PIN-pairing / request-access dialogs
   ui_settings.rs          resolution · refresh · decoder · bitrate · compositor · mic
   ui_stream.rs            the stream window (GtkGraphicsOffload present) + input capture
-  launch.rs · session.rs  session launch/UI glue; lifecycle over the NativeClient connector
-  video.rs                FFmpeg VAAPI / software decode → dmabuf / texture
-  audio.rs                PipeWire playback + mic uplink
-  gamepad.rs · keymap.rs  SDL3 controllers + feedback; keyboard VK mapping
-  trust.rs · discovery.rs persistent identity, known hosts + settings, mDNS browse
-  library.rs              mgmt-API library client (mTLS + pinned fingerprint, art proxy)
+  launch.rs               session launch/UI glue over the shared session pump
+  video_gl.rs             VAAPI dmabuf → RGBA GL presenter (EGL import, CICP-driven CSC)
 tools/screenshots.sh      store screenshot capture (app self-capture; Xvfb fallback)
 ```
 
+The UI-agnostic plumbing — session pump, FFmpeg decode, PipeWire audio, SDL3 gamepads +
+keymap, trust store, mDNS discovery, library client, Wake-on-LAN — lives in
+`crates/pf-client-core`, shared with the Vulkan session binary.
+
 ## Related
 
 - **[Documentation](https://docs.punktfunk.unom.io)** — quick start, pairing, troubleshooting