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>

crates/pf-client-core/Cargo.toml

@@ -0,0 +1,36 @@
+[package]
+name = "pf-client-core"
+description = "Shared Linux-client plumbing — session pump, FFmpeg decode, PipeWire audio, SDL3 gamepads, trust store, discovery — extracted from the GTK client so the shell and the Vulkan session binary build on one implementation"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+authors.workspace = true
+repository.workspace = true
+
+# Same Linux gating as clients/linux: `cargo build --workspace` stays green on macOS
+# (the Mac client lives in clients/apple); elsewhere this crate is `wol` plus stubs-free
+# emptiness. `wol` is pure std and stays cross-platform, matching the old main.rs.
+[target.'cfg(target_os = "linux")'.dependencies]
+punktfunk-core = { path = "../punktfunk-core", features = ["quic"] }
+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"] }
+
+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"