Centralize SQLite infrastructure and migrations

[itsDNNS]

Summary

• centralize SQLite connection policy and explicit read/write transaction ownership
• add atomic bulk writes and migrate core plus module storage callers to the shared contract
• introduce ordered, shape-aware migrations for fresh, current, legacy, hybrid, and unknown database shapes
• harden backup and restore with consistent copies, staged integrity checks, atomic publication, and WAL/SHM cleanup
• enforce ownership boundaries with focused policy, transaction, migration, restore, and static contract tests

Validation

• python -m pytest tests/ -q --tb=short --ignore=tests/e2e — 3797 passed, 2 skipped
• Chromium E2E, isolated file batches — 531 passed with exact 531-test denominator
• focused migration, storage, backup, and ownership tests — 92 passed
• 5,000-event bulk benchmark — one commit, one executemany, 0.027s wall time, 513 KiB peak memory
• python -m compileall -q app tests
• git diff HEAD^ HEAD --check

Compatibility

Existing storage method signatures and the connect_sqlite compatibility seam remain unchanged. The migration registry is additive, the existing UTC migration remains separate, and no dependency, retention, synchronous-policy, or user-facing schema change is included.