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>

docs/windows-client-bootstrap.md

@@ -5,6 +5,29 @@ and live-validated on a real RTX 4090; the client is the remaining piece. This d
 starting point: the locked decisions, the reference code to port, the stack swaps, the dev loop, and
 the gotchas. Read it top to bottom, then start at **Phase 1** (de-risk Reactor first).
 
+## Status — stage 1 landed (2026-06-15)
+
+The client is implemented in `crates/punktfunk-client-windows` (binary `punktfunk-client`) and is
+**build + clippy + fmt + test green on `x86_64-pc-windows-msvc`** (built on the dev VM). Done: winit
+window + **Direct3D11 flip-model swapchain** present (WARP on the GPU-less box; runtime-compiled
+fullscreen-triangle shaders, Contain-fit letterbox), **FFmpeg software HEVC decode**, **WASAPI** render
++ mic capture, keyboard/mouse/wheel capture (physical-`KeyCode`→VK, click-to-capture), **SDL3**
+gamepads, `mdns-sd` discovery, and the full trust surface (identity + TOFU + SPAKE2 PIN over
+`--connect`/`--discover`/`--pair`/`--headless`).
+
+- **Reactor was evaluated and rejected** (a research pass + the points below): windows-rs Reactor
+  ships **no `SwapChainPanel` and no `ISwapChainPanelNative::SetSwapChain` escape hatch**, so it
+  cannot host a DXGI presenter. The client uses the doc's sanctioned fallback — **winit + a raw
+  D3D11 swapchain on the HWND** — which builds and runs against WARP on the GPU-less VM. A native
+  WinUI look would need the `SwapChainPanel` hatch to land upstream first.
+- **Build gotcha (in addition to the ASCII *output* path below):** `CARGO_HOME` itself must be on an
+  **ASCII path** (e.g. `C:\Users\Public\.cargo`). SDL3's `build-from-source` compiles a precompiled
+  header whose `#include` embeds the registry source path; the `ü` in the dev box's username makes
+  MSVC's PCH/structured-output fail (`MSB8084` / `C4828`). Set `CARGO_HOME=C:\Users\Public\.cargo`.
+- **Still pending:** live host validation (the dev box has no GPU → glass-to-glass numbers defer to
+  the RTX box), **D3D11VA hardware decode** + **10-bit/HDR present**, a native host-list/settings
+  GUI (CLI flags for now), and RAWINPUT relative-mouse pointer-lock. Phases 4–7 below are the map.
+
 ## What we're building
 
 A native Windows client that connects to a punktfunk/1 host (`serve --native` / `m3-host`), decodes