feat(windows-client): SDL3 gamepads + docs — full stage-1 parity, MSVC-green

Adds the SDL3 gamepad service (near-verbatim port of the GTK client's — SDL3 is
cross-platform) and wires it into the winit app: per-session capture (buttons/axes,
DualSense touchpad + motion 0xCC), feedback (rumble, lightbar, raw DualSense effects),
single-pad-forwarded model with auto pad-type from the physical controller. Built from
source on Windows (no system SDL3).

- gamepad.rs: GamepadService (app-lifetime SDL thread) attach/detach on session
  connect/end; auto_pref resolves "Automatic" to the attached pad's type.
- app.rs: hold the service, attach on Connected, detach on Ended/Failed/close. Also
  simplify the keydown path (drop the identical if/else arms).
- main.rs: start the service for the windowed path, resolve GamepadPref from settings +
  the physical pad.

Build gotcha documented + fixed in the dev loop: SDL3's build-from-source MSVC
precompiled-header chokes on the `ü` in the dev box's username embedded in the cargo
registry path (MSB8084/C4828) — CARGO_HOME must be an ASCII path
(C:\Users\Public\.cargo). Unrelated to our code.

Docs: CLAUDE.md M4 + docs/windows-client-bootstrap.md status banner (winit-not-Reactor
rationale, CARGO_HOME gotcha, what's pending) + docs-site clients.md "Windows desktop
client (in development)". Crate is build + clippy + fmt + test green on
x86_64-pc-windows-msvc.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CLAUDE.md

@@ -112,6 +112,21 @@ Low-latency desktop/game streaming stack, Linux-first, with a shared Rust protoc
    Intel/AMD client box to live-verify the hw path. Next: the stage-2 raw-Wayland
    presenter (wp_presentation feedback, tearing-control, Vulkan Video on NVIDIA) —
    **wgpu/winit rejected** (no dmabuf import / presentation feedback / shortcuts-inhibit).
+   **Windows stage 1 done 2026-06-15** (`crates/punktfunk-client-windows`, binary
+   `punktfunk-client`): pure-Rust **winit + Direct3D11 flip-model swapchain** present (WARP
+   fallback for the GPU-less dev box; runtime-compiled fullscreen-triangle shaders, Contain-fit
+   letterbox), **FFmpeg software HEVC decode** (D3D11VA hw decode is the follow-up), **WASAPI**
+   shared-mode render + mic capture, keyboard (physical-`KeyCode`→VK) + absolute mouse + wheel
+   capture (Moonlight-style click-to-capture, Ctrl+Alt+Shift+Q release), **SDL3** gamepads
+   (rumble/lightbar/DualSense, built from source), `mdns-sd` discovery, shared client identity
+   + TOFU + SPAKE2 PIN pairing (`--connect`/`--discover`/`--pair`/`--headless`). Builds + clippy
+   + fmt + tests green on `x86_64-pc-windows-msvc` (built on the dev VM). **UI = winit + raw
+   D3D11, NOT WinUI3/Reactor** — a research pass confirmed windows-rs Reactor ships no
+   `SwapChainPanel`/`SetSwapChain` escape hatch, so it can't host the presenter (the bootstrap
+   doc's sanctioned fallback). Gotcha: `CARGO_HOME` must be an ASCII path — the `ü` in the dev
+   box's username breaks SDL3's MSVC precompiled-header build. Next: live host validation
+   (no GPU on the dev box → glass-to-glass defers to the RTX box), D3D11VA hw decode + 10-bit/HDR
+   present, a native host-list/settings GUI, and RAWINPUT relative-mouse pointer-lock.
 2. **Sub-frame pipelining**: overlap encode and transmit within a frame. Requires a direct
    NVENC SDK wrapper (libavcodec only emits whole AUs) — the next big latency lever (~2–4 ms
    at high res).