XY-524: Add optional local privacy classifier gate for public projections

[yvette-carlisle]

Summary

• Add a local-only public projection privacy classifier adapter with disabled-by-default config and loopback-only HTTP validation.
• Route Linear execution-event public projections through prepared classifier output before publishing or caching.
• Document the classifier as a secondary guard and add deterministic fake-classifier tests for allow, suspicious, and unavailable cases.

Validation

• cargo make fmt
• cargo make lint-fix
• cargo make test (814 passed, 1 skipped)