OIC versioned knowledge API #228

Context

The API is the product boundary. The UI (#229, #230) and the reviewer (#234) use only this API. Depends on #225 and #227.

Behavior to implement

Versioned under /oic/v1:

• Investigations: create, list, status, events; post a message or answer; cancel or pause.
• Proposals: list; approve, reject with a reason, edit, request further investigation.
• Knowledge: claims, entities, evidence, and claim history. Filters: scope, entity, claim type, predicate, status, valid time ("as of"), evidence type, related repo, service, or test.
• Context query for downstream agents: input is repo, changed paths, affected services or entities, and an optional change description. Output is relevant claims with their metadata.
• Every claim response carries its epistemic metadata: type, scope, status, valid and recorded time, last verified, supporting and contradicting evidence references, related claims, provenance, and stale, disputed, or superseded flags. Never plain text alone.
• No provider identifiers in knowledge responses.

Acceptance criteria

• OpenAPI docs are published, and error responses are documented.
• Contract tests for the context query, which the reviewer depends on.
• Claims can be retrieved with no agent running.