feat(harness): add surface-aware harness selection

[solomonneas]

Summary

• Add SurfaceRecord and surface-aware Selection so cursor-cli and cursor-gui keep separate fixture evidence while projecting through the shared cursor harness.
• Gate install_selection on conformance availability: refuse externally_blocked / binary_not_found and external_only surfaces unless --projection-only is explicit; persist per-surface evidence to .brigade/surface-evidence.json.
• Extend brigade harness install with --surface and --projection-only, returning typed CLI errors instead of tracebacks.

Closes #344.

Test plan

• brigade work verify run --target . --command "pytest -q tests/test_surface_aware_install.py" --capture brigade-work
• brigade work verify run --target . --command "./scripts/verify" --capture brigade-work
• Native (available), external-only (cursor-gui), and blocked-binary (binary_not_found) fixtures covered in tests/test_surface_aware_install.py
• Separate cursor-cli / cursor-gui capability evidence preserved after install

Made with Cursor

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