SQLite-backed durable state for vibesurfer.

The store owns one SQLite database file at ~/.vibesurfer/state.db (or in-memory for tests). It is the source of truth for every piece of cross-restart state: sessions, pages, refs, marks, annotations, the audit log, encrypted auth blobs, and the skill cache. The daemon's in-memory caches are derivative — on restart they are rebuilt from this crate.

Layout

• [Store] — the main handle. CRUD methods for every table.
• [types] — owned domain types mirroring the SQL schema.
• [auth] — AES-256-GCM helpers and master-key resolution (OS keyring → ~/.vibesurfer/key).
• [error::StoreError] — every fallible function returns this.
• [migrate] — the migration runner; called automatically by [Store::open].