A local-first note taking app

Vault integration phase 1: foundation types, HabitatRepo, snapshot, and utils master

Lays the groundwork for Obsidian-style vaults backed by Habitat PDS + libp2p gossipsub. Adds types, HabitatRepo/DocHandle adapter over AutomergeDocSession, VaultSnapshotManager, vault registry, and utility modules (content hashing, text diff, move detection similarity, directory traversal). Also pulls forward collection-aware routing in automergeDoc.ts and adds changeAt to AutomergeDocSession. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>