v2: Snapshot live SQLite stores consistently before querying

[jmcte]

Problem / intent

Several providers query live Apple SQLite databases directly. A live database can have committed state split across the main DB, WAL, and SHM files, and readers currently use duplicated blocking sqlite3 subprocess paths without a shared timeout or cleanup contract.

This v2 issue introduces one privacy-safe, consistent snapshot/query utility before incremental archives or native-provider fallbacks expand.

Acceptance criteria

• Copy the source DB and any present -wal / -shm companions into a private temporary directory before querying.
• Preserve a consistent read-only view without modifying, checkpointing, locking, or vacuuming the Apple-owned source.
• Enforce query-only/read-only behavior, a busy timeout, a bounded process/query timeout, and deterministic cleanup.
• Return structured missing-store, permission-denied, unsupported-schema, locked-store, and timeout failures.
• Migrate Messages and Safari history first; document the remaining providers to migrate.
• Add synthetic tests for WAL-backed rows, a locked/busy store, missing companion files, cleanup, schema drift, and permission failures.
• Never log or retain copied private-store contents.

Validation

swift test
bash scripts/ci/run-fast-checks.sh

Dependencies

• Uses the provider identity/health model from v2: Define a versioned provider capability manifest #89 where practical.
• Foundation for provider archives, Messages search, and private-store fallbacks.

Related

• v2 follow-up to the private-store readers added under closed issues Add Safari browsing history command #25 and Add iMessage / Messages conversation inventory command #26.