chore(pf-capture): make the crate verifiable — Windows CI lint + two denies (sweep Phase 0)

Gate for the rest of design/pf-capture-sweep.md: today half this crate is compiled by no CI job
at all, so the Windows-side findings can't even be type-checked.

0.1 (X1) — windows-host.yml lints `-p pf-capture --all-targets`. The host lint above it builds
pf-capture only as a DEPENDENCY, so its `#[cfg(test)]` modules were never compiled anywhere: the
5 StallWatch tests, the DXGI HDR self-tests and the cursor-conversion tables were dead code in
CI. The workflow's own comment already diagnosed this blind spot and fixed it for pf-encode;
pf-capture never got the same treatment. No features on this crate, so no feature juggling and
no extra dep tree.

0.2 (X2) — `#![deny(unsafe_op_in_unsafe_fn)]` beside the existing
`deny(clippy::undocumented_unsafe_blocks)`. The crate declares "every unsafe block carries a
SAFETY proof; enforce it" in ten file headers, but in edition 2021 that lint has nothing to fire
on inside an `unsafe fn` — so the hardest FFI in the crate was exempt from its own program: the
ring/slot construction, the fence signal, the blend scratch, and every D3D converter ctor/convert.
119 operations across 16 functions now carry a proof. `shared_object_sa` loses its `unsafe`
marker instead (it states no precondition — only its RESULT is a raw pointer, which is the
caller's business).

0.3 (X4) — drop the crate-wide `#![allow(dead_code)]`. Verified: zero warnings on either target
without it, so it was hiding nothing the lint can see (W16's dead items are `pub`/written-once,
so they need Phase 1.7's deletion instead).

No behaviour change: only lint attributes, `unsafe { }` scoping and comments.

Linux `cargo test -p pf-capture` 6/6, clippy --all-targets clean on both targets (Windows
verified by cross-checking x86_64-pc-windows-msvc locally).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitea/workflows/windows-host.yml

@@ -172,12 +172,15 @@ jobs:
         # openh264 rebuild), and keeps everything in one C:\t\release tree. Same reason
         # pf-vkhdr-layer's clippy below runs --release.
         #
-        # pf-encode is linted SEPARATELY with --all-targets so its Windows `#[cfg(test)]` modules
-        # are type-checked — the AMF C-ABI layout assertions (`variant_layout_matches_c` and
-        # friends, which are the only guard on a hand-mirrored vtable ABI), the QSV tests, and the
-        # PyroWave-Windows smoke test. The host lint above cannot cover them: `-p punktfunk-host`
-        # only builds pf-encode as a dependency, so its test targets are never compiled, and that
-        # blind spot is what let the Linux twin's tests rot to the wrong arity unnoticed.
+        # pf-encode and pf-capture are linted SEPARATELY with --all-targets so their Windows
+        # `#[cfg(test)]` modules are type-checked — pf-encode's AMF C-ABI layout assertions
+        # (`variant_layout_matches_c` and friends, which are the only guard on a hand-mirrored
+        # vtable ABI), the QSV tests, the PyroWave-Windows smoke test; pf-capture's `StallWatch`
+        # tests, the DXGI HDR self-tests and the cursor-conversion tables. The host lint above
+        # cannot cover them: `-p punktfunk-host` only builds those crates as dependencies, so their
+        # test targets are never compiled anywhere, and that blind spot is what let the Linux twin's
+        # tests rot to the wrong arity unnoticed. pf-capture has no cargo features, so it needs no
+        # feature juggling and pulls in no extra dep tree.
         # NOTE: clippy (a check, no link step) is deliberately the vehicle here — `cargo test`
         # with `nvenc` cannot LINK on MSVC: nvidia-video-codec-sdk link-imports
         # NvEncodeAPICreateInstance / NvEncodeAPIGetMaxSupportedVersion, which resolve only against
@@ -188,6 +191,7 @@ jobs:
         run: |
           cargo clippy --release -p punktfunk-host --features nvenc,amf-qsv,qsv -- -D warnings; if ($LASTEXITCODE) { throw "host clippy" }
           cargo clippy --release -p pf-encode --all-targets --features nvenc,amf-qsv,qsv -- -D warnings; if ($LASTEXITCODE) { throw "pf-encode clippy" }
+          cargo clippy --release -p pf-capture --all-targets -- -D warnings; if ($LASTEXITCODE) { throw "pf-capture clippy" }
           cargo clippy --release -p punktfunk-tray -- -D warnings; if ($LASTEXITCODE) { throw "tray clippy" }
 
       - name: Build + lint the HDR Vulkan layer (pf-vkhdr-layer)