fix: native Windows Workstream creation and persistence

[MelaBuilt-AI]

Summary

• Fix native Windows worktree registration comparison by resolving Git's forward-slash paths before comparing with the canonical native path.
• Derive receipt-relative paths from the validated parent so Windows short-name aliases do not produce traversal-shaped receipts.
• Open owned persistence files read/write for fsync, fixing native cancellation EPERM without truncation or weakened error checks.
• Translate bounded WorktreeAuthority errors to useful conflict/unavailable responses; never expose raw Git failure stderr.
• Add a real-Git packaged API create/restore/cancel regression, run it in core CI, and add a real API error regression.
• Advance Windows setup metadata to windows.3 / 0.15.0.5, retaining AppId/destination/state.

Verification

• Shipped native Windows package regression RED: POST Workstreams returned 500 instead of201.
• Native isolated corrected modules GREEN: create201, restore current, cancel200/removed, Git registration count back to one. Includes Windows short-name TEMP path.
• Full local check:core PASS with isolated XDG data; packaging Python and Node launcher/helper/workstream tests PASS.
• No automated product-navigation journeys, external harness dispatch, or operator lane changes.

Delivery gates

After exact-head green CI: merge, require separate merged-main green CI, rebuild private Windows ZIP/setup and Linux DEB/tar; then separately repin/repack/test npm against exact archive bytes. No public binaries, packaging workflow dispatch, Release, npm publication, provider changes, or TEST45495 changes. Native installer/operator acceptance remains separate.