docs: rework client/crate READMEs, add missing ones

Rework the client READMEs to be accurate and inviting to first-time
visitors, and fill in the gaps where crates and tools had none.

- Rewrite clients/{apple,android,decky} READMEs (features-first, trim
  dense internal narrative; drop the stale "one session at a time" /
  "renegotiation not implemented" section from the Apple README).
- Add READMEs for clients/{linux,windows,probe}, which had none.
- Add crate READMEs for punktfunk-host, punktfunk-core, pf-driver-proto.
- Add brief READMEs for tools/{loss-harness,latency-probe}.
- Fix packaging/README duplicate "Option B" heading (bootc -> Option C).
- Fix docs-site/README stale docs/ -> design/ reference.
- De-stale packaging/windows/drivers/pf-dualsense README (drop "M0 spike"
  / external-checkout framing; reflect in-tree workspace + shipped +
  installer-bundled + multi-pad), keeping the driver-authoring lore.

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

clients/windows/README.md

@@ -0,0 +1,71 @@
+# punktfunk — Windows client
+
+The native **Windows** app for streaming a punktfunk host to your PC. A modern WinUI 3 app that
+discovers hosts on your network, pairs with a PIN, and streams at your display's own resolution and
+refresh rate — with a hardware-accelerated D3D11 video path and HDR.
+
+It's **pure Rust**: the UI is WinUI 3 driven through [windows-reactor](https://github.com/microsoft/windows-rs)
+(a declarative, React-like framework), and it links the shared **`punktfunk-core`** directly to speak
+the fast **`punktfunk/1`** protocol.
+
+## Features
+
+- **Hardware decode, GPU present** — FFmpeg HEVC with a **D3D11VA zero-copy path** (decoder and
+  presenter share one D3D11 device; NV12/P010 textures sampled straight into a `SwapChainPanel`
+  composition swapchain), with a robust software-decode fallback.
+- **HDR10** — advertise 10-bit/HDR, detect PQ in-band, and flip the swapchain to `R10G10B10A2` +
+  ST.2084 with HDR10 metadata.
+- **Your display's native mode** — the host builds a virtual display at exactly your WxH@Hz.
+- **Audio both ways** — WASAPI render + mic capture.
+- **Full controller support** — SDL3 gamepads with rumble, lightbar, and DualSense feedback.
+- **Find hosts automatically** — mDNS discovery lists hosts on your LAN, alongside saved and manual
+  entries. First connect does a one-time **SPAKE2 PIN pairing** (or TOFU on trusted LANs), then
+  reconnects on a pinned identity.
+- **Polished shell** — host cards, settings (resolution / refresh / decoder / bitrate / HDR / mic),
+  a status-chip stream HUD, and the full trust surface. Stream input uses Win32 low-level hooks with
+  a Ctrl+Alt+Shift+Q capture toggle.
+
+Builds and ships for both **x64** and **ARM64** as a signed **MSIX**.
+
+## Get it
+
+Install the signed MSIX from the package registry — see
+**[docs.punktfunk.unom.io/docs/install-client](https://docs.punktfunk.unom.io/docs/install-client)**.
+A stock [Moonlight](https://moonlight-stream.org/) client also works over GameStream if you prefer.
+
+## Build from source
+
+Windows-only (the crate builds as a stub on other platforms so the workspace stays green). You need
+the MSVC toolchain, an `FFMPEG_DIR` FFmpeg tree, and CMake (SDL3 builds from source). windows-reactor's
+`build.rs` downloads the Windows App SDK NuGets and needs `CARGO_WORKSPACE_DIR` set.
+
+```sh
+cargo build -p punktfunk-client-windows --target x86_64-pc-windows-msvc
+
+# CLI paths for testing (no window):
+punktfunk-client --discover                                   # list hosts on the LAN
+punktfunk-client --headless --connect host[:port] [--pin HEX] # connect, count frames, print stats
+```
+
+> `CARGO_HOME` must be an ASCII path — non-ASCII characters break SDL3's MSVC precompiled-header
+> build. Packaging (MSIX manifest, signing) lives in [`packaging/`](packaging/).
+
+## Layout
+
+```
+src/
+  main.rs · app.rs        entry point + CLI paths; WinUI 3 shell (windows-reactor)
+  present.rs · gpu.rs      SwapChainPanel D3D11 composition swapchain; shared D3D11 device
+  video.rs                FFmpeg HEVC decode (D3D11VA zero-copy + software fallback)
+  audio.rs                WASAPI render + mic capture
+  gamepad.rs              SDL3 controllers + rumble/lightbar/DualSense feedback
+  input.rs                Win32 low-level keyboard/mouse hooks → host input
+  session.rs              session lifecycle over the NativeClient connector
+  trust.rs · discovery.rs persistent identity, TOFU/PIN pairing, mDNS browse
+packaging/                MSIX manifest, signing, pack script
+```
+
+## Related
+
+- **[Documentation](https://docs.punktfunk.unom.io)** — quick start, pairing, troubleshooting
+- **[Project README](../../README.md)** — the host, the other clients, and how it all fits together