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/Cargo.toml

@@ -15,6 +15,10 @@ path = "src/main.rs"
 # Everything is Linux-gated so `cargo build --workspace` stays green on macOS (the Mac
 # client lives in clients/apple); on other platforms this builds as a stub binary.
 [target.'cfg(target_os = "linux")'.dependencies]
+# Session pump, decode, audio, gamepads, trust, discovery, keymap — the UI-agnostic
+# plumbing, shared with the upcoming Vulkan session binary (design: punktfunk-planning
+# linux-client-rearchitecture.md). This crate keeps only the GTK shell + GL presenter.
+pf-client-core = { path = "../../crates/pf-client-core" }
 punktfunk-core = { path = "../../crates/punktfunk-core", features = ["quic"] }
 
 # UI shell. GraphicsOffload needs GTK ≥ 4.14; black-background ≥ 4.16. AlertDialog/
@@ -23,25 +27,10 @@ gtk = { package = "gtk4", version = "0.11", features = ["v4_16"] }
 adw = { package = "libadwaita", version = "0.9", features = ["v1_5"] }
 async-channel = "2"
 
-# Video decode (same FFmpeg pin as the host) and audio.
-ffmpeg-next = "8"
-opus = "0.3"
-pipewire = "0.9"
-
-# Gamepads: capture + feedback (full DualSense fidelity — touchpad/motion/triggers/LEDs
-# need the hidapi driver).
-sdl3 = { version = "0.18", features = ["hidapi"] }
 # The VAAPI GL presenter (video_gl.rs): EGL dmabuf import into a GDK-shared context, dlopened
 # at runtime (`dynamic`) so GPU-less boxes and the software path never touch libEGL.
 khronos-egl = { version = "6", features = ["dynamic"] }
 
-mdns-sd = "0.20"
-# Game-library fetch from the host's management API over mTLS + fingerprint pinning.
-# `ureq` is small + sync (the host uses it too) and its rustls unifies with the
-# workspace's (quinn's) 0.23; the pinning verifier mirrors core's private `PinVerify`.
-ureq = "2"
-rustls = { version = "0.23", features = ["ring"] }
-serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 anyhow = "1"
 tracing = "0.1"