Add DB-backed worktree inventory table and repository

[chubes4]

Goal

Add a DMC-owned database table/repository for known workspace worktrees so DMC does not have to rediscover everything from filesystem scans on every operator command.

Scope

• Add activation/schema management for datamachine_code_worktrees.
• Add repository/service for upsert/list/get/delete by handle.
• Write rows from worktree add, finalize, mark-cleanup-eligible, remove, prune, and metadata refresh paths.
• Add workspace inventory refresh or equivalent to reconcile DB from current filesystem inventory.
• workspace hygiene should report DB inventory freshness and optionally refresh.

Required behavior

• Handle remains the stable key.
• Filesystem metadata can be imported, but DB becomes the queryable source.
• Missing path / stale row state is recorded instead of silently disappearing.
• No long-term compatibility shim. Unknown unmanaged paths require explicit adoption/refresh.

Tests

• Schema install smoke.
• Worktree add writes DB row.
• Finalize updates lifecycle/pr fields.
• Remove/prune marks/removes row.
• Inventory refresh reconciles missing/new rows deterministically.