Connect Session Watcher privacy filtering and approved-update handoff - #3132

Connect the Session Watcher scaffold to an injected privacy filter and approved-update destination. The watcher now fails closed unless the required dependencies are supplied, and publishing requires a watcher-owned approval handle rather than the original raw update. This PR targets the scaffold branch from #3129; it does not implement a privacy policy or real Neumem ingestion.

• Add optional filter and destination dependencies while preserving new SessionWatcher() and all unrelated stubs.
• Pass the whole normalized update through filtering, including events, paths, identity and metadata; treat null as deliberate exclusion.
• Keep approved data behind per-instance, runtime-checked opaque handles; reject raw, copied, forged and foreign approvals.
• Snapshot input, approved output and each delivery to isolate mutations. Node V8 serialization rejects shared-memory buffers and uncloneable payloads.
• Surface distinct configuration, filtering, invalid-result, snapshot and delivery errors without sensitive payloads or dependency causes.
• Document the handoff contract, trusted-dependency boundary and destination acceptance semantics, independent of capture checkpoints and downstream extraction.
• Add regression coverage and the explicit Jest ESM dev dependency; leave capture/event types, normalization, lifecycle, daemon and hooks unchanged.

Validation: package npm run build passed; all 29 tests across 3 suites passed via npm run jest-esm -- --runInBand --testPathPattern='.*[.]spec[.]js'. Changed-file Prettier, lint, complexity (25/30 thresholds), circular-dependency and debt gates passed against origin/georgeng/git-story-session-watcher-stubs (merge base e3ecf6eae). Circular dependencies remain 220 → 220. Validation uses injected test doubles, not a production privacy policy or live Neumem service.