fix(release): build and publish Windows x86_64 wheels

[ashishpatel26]

Summary

• release.yml's wheel matrix never had a Windows target — only linux x86_64/arm64 and macOS arm64 wheels are built. No Windows wheel has ever shipped, so pip install headroom-ai on Windows falls back to source (or fails outright), leaving headroom._core missing and every compressor silently no-op'ing (compress() catches ModuleNotFoundError and returns input unchanged).
• Rust side is already Windows-ready: dynamic ORT loading via ort-load-dynamic on cfg(windows) landed for the AVX2 SIGILL fix (fix(core): load ONNX Runtime dynamically so headroom._core imports on non-AVX2 x86-64 #1715), and ort-sys ships prebuilt ONNX Runtime binaries for x86_64-pc-windows-msvc — no CMake/source build needed the way x86_64-apple-darwin requires.
• Adds a windows-2022 / x86_64-pc-windows-msvc row to build-wheels, plus a matching smoke-import-wheels entry (PowerShell) that installs the built wheel into a clean venv and imports headroom._core, gating publish the same way the Linux/macOS rows do.

Fixes #1144 (Bug 1 — missing Windows wheel).

Bug 2 in that issue (headroom --help crashing with ModuleNotFoundError: fastapi on a core-only install) is already fixed on main: headroom.proxy.server is lazily imported inside the proxy command, not at CLI module load time. Verified locally by invoking headroom --help with fastapi import blocked via a meta-path finder — exits 0.

Test plan

• tests/test_release_workflows.py — 28 passed, 1 pre-existing unrelated failure (test_no_native_tls_in_wheel_build_tree, reproduces on clean main too — local cargo tree environment issue)
• .github/workflows/release.yml parses as valid YAML
• Verified headroom --help doesn't require fastapi on current main (Bug 2 already fixed)
• CI run of the new build-wheels / smoke-import-wheels Windows matrix rows on this PR (release.yml triggers a dry-run on PRs touching crates/headroom-py/**... this PR only touches release.yml itself, which is also in the path filter, so the dry-run should fire)

[github-actions]

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[ashishpatel26]

Closing — duplicate. Upstream already fixed this in #1335 (merged 2026-06-24), which added a more thorough windows-latest wheel row (explicit actions/setup-python, better abi3 fallback matching) than what I proposed here. Issue #1144 (Bug 1) is resolved by that merge; just needs the issue closed/labeled stale.