refactor: extract shared consolidation drain helpers to reduce duplication

[dnnspaul]

Summary

• Adds process-inbox CLI command that runs the full pipeline (upload → consolidate → synthesize) in one shot
• Extracts the duplicated consolidation drain loop, embedding check, and KB synthesis pass into shared helpers in src/commands/consolidation-drain.ts
• Refactors both consolidate and process-inbox commands to use the shared helpers, eliminating ~80 lines of duplicated logic

Details

The consolidation drain loop (lock acquisition with timeout, batch processing, error handling) and the KB synthesis pass were copy-pasted between consolidate.ts and process-inbox.ts. This PR extracts three reusable functions:

• runEmbeddingCheck(activation) — non-fatal embedding model consistency check
• drainConsolidation(consolidation) — full drain loop with lock timeout, returns aggregate stats
• runSynthesisPass(consolidation) — locked synthesis with non-fatal error handling

The server-side runConsolidationDrain in index.ts is intentionally left as-is — it has different semantics (shutdown-aware, exponential backoff, logger vs console).

Verification

• tsc --noEmit — clean
• biome check — clean on all changed files
• bun test — 498 pass, 1 pre-existing failure (config-file test, unrelated)