feat(server): expose read-only extraction diagnostics

[PsiACE]

Which issue or RFC does this PR close?

Related: Artifact Processing Supervisor RFC.

Rationale for this change

A capability boolean cannot distinguish missing extraction configuration, model failures, and worker crashes.

What changes are included in this PR?

• Expose independent extraction configuration, Supervisor state, and local observations in capabilities.
• Retain failure evidence across later successes and classify errors without exposing provider messages.
• Update OpenAPI, generated models, English/Chinese operating docs, and behavior tests.

Are there any user-facing changes?

GET /v1/capabilities adds a read-only extraction snapshot without model probes or diagnostic database queries. External configuration and execution state remain unknown. Observations start unverified and reset with the Runtime; historical success or failure is not a current health verdict. No migration.

How was this change tested?

• make check
• make contract-test (49 passed)
• Extraction, Supervisor, composition, metrics, Server, and CLI regression suites (137 passed).
• make e2e-test (316 passed, 64 skipped)
• make docs-test

Tests cover missing configuration, model errors, worker crashes/timeouts, leader/standby roles, discovery failures, retained history, no-op flushes, and restart semantics. Model failures were injected; worker crash/timeout tests used real child processes. Lease-role tests used SQLite. No live model calls.

AI usage statement

Codex (GPT-6) assisted with implementation, tests, and PR preparation.