feat(observability): support native Windows hooks

[BjRo]

Why

The Langfuse backend and registered Codex hooks were limited to Unix because the manifest required Bash and the backend imported fcntl. Native Windows users could not capture or export telemetry without WSL. Closes #205.

What changed

Add a native PowerShell launcher selected through commandWindows, replace Unix-only locking with a locked cross-platform dependency, and preserve durable state behavior where Windows cannot fsync directories. Extend packaged-hook, failure, concurrency, fresh-install, and CI coverage to native Windows; document the platform prerequisites and release version 0.6.0.

Verification

• bun run check:python — passed; observability package: 141 tests, 98.50% statement coverage, 95.07% branch coverage.
• uv run --quiet --frozen --no-dev --project plugins/capability/darrow-observability-langfuse/backend python plugins/capability/darrow-observability-langfuse/backend/tests/fresh_install.py — passed.
• bun run check:python:performance — passed.
• scripts/test-python-quality-changes — passed.
• bun run check:docs, bun run lint, bun run lint:shell, bun run lint:ts, bun run typecheck, and bun run check:decisions — passed.
• bun test — 631 passed, 1 unrelated discovery eval assertion failed; the focused rerun reproduced it.

Review notes

Native Windows execution is covered by the new Windows Python matrix and copied-plugin job; those hosted checks are the authoritative PowerShell validation. The unrelated failing test is discovery eval loopholes > planning transfer does not turn missing repository policy into authority in evals/runner/discovery-eval-checks.test.ts.

Checklist

• I have read and followed CONTRIBUTING.md, including the contribution
  licensing terms.
• I added or updated the applicable invariant before implementation, or
  this change does not affect a capability invariant.
• I added or updated colocated evals, or this change does not affect skill
  behavior.
• I confirmed that each changed plugin remains self-contained, or this
  change does not affect plugin content.
• I ran bun run check:python, or this change does not affect registered
  Python packages or their repository quality infrastructure.