Windsurf hook install script

[blitzcrieg1]

Windsurf is on the roadmap and uses a lifecycle-hook model similar to Cursor. Wiring it needs an install script parallel to the existing ones.

Task

Add scripts/install_windsurf_hooks.ps1, modeled on scripts/install_cursor_hooks.ps1, that non-destructively registers scripts/agentmetry_ingest.py as Windsurf's tool hook. Document the one-liner in the README "Wire your IDEs" section.

Acceptance criteria

• Installs the hook without clobbering existing Windsurf config; idempotent (safe to re-run).
• A short note in docs/agentmetry-external-ingest.md.

Needs a Windsurf install to test — hence help wanted rather than good first issue.