feat(incident-detective): constrain case generation - #9

Summary

• add versioned inputs for bounded case generation, internal Case Proposals, and explicit human review
• add a provider-neutral incident-detective.case-proposal-v1 operation with deterministic post-processing
• validate evidence DAGs, reachable budget paths, real evidence tradeoffs, counterevidence, read-only access, privacy, and caller-owned constraints
• keep model output review-only and permanently non-publishable; server-owned safety notes cannot be relaxed by the model
• complete P2-005 fixtures, documentation, schema registry, and TODO state

Safety boundary

• the Provider never receives evidence payloads, internal answers, canonical attempts, or scoring rules
• invalid/sensitive inputs fail before the Provider call
• invalid proposals receive at most one bounded retry and are otherwise discarded
• an approved human review still returns publishable: false
• this change adds no live Provider, HTTP route, UI action, GitHub write, deployment, storage, or analytics

Validation

• npm run validate
• 16 test files / 193 tests passed
• production Astro build passed
• 38 static contracts passed