fix: add SQLite schema versioning for future migrations

[datlechin]

Summary

Adds PRAGMA user_version-based schema migration infrastructure to both SQLite databases (query_history.db and sql_favorites.db).

Both databases currently use CREATE TABLE IF NOT EXISTS with no version tracking. If a future release needs to add a column, existing users would silently keep the old schema. This PR sets the foundation so future schema changes can use ALTER TABLE ... ADD COLUMN migrations gated by version checks.

Changes:

• QueryHistoryStorage.swift — Added migrateIfNeeded(), getUserVersion(), setUserVersion(). Current schema set to version 1.
• SQLFavoriteStorage.swift — Same three methods added. Current schema set to version 1.

No schema changes are made — this just stamps the current schema as version 1 so future migrations have a baseline.

Addresses audit item C5.

Test plan

• Fresh launch: sqlite3 ~/Library/Application\ Support/TablePro/query_history.db "PRAGMA user_version;" returns 1
• Fresh launch: sqlite3 ~/Library/Application\ Support/TablePro/sql_favorites.db "PRAGMA user_version;" returns 1
• Query history works normally (execute queries, search history)
• SQL favorites work normally (create/edit/delete favorites and folders)
• Existing tests pass