Adds SqlWriter: a pyodbc-backed writer that dedup-inserts into
dbo.SyncQueue (IF NOT EXISTS guarded by UX_SyncQueue_Dedup), invokes
dbo.usp_SyncApply, and reports applied SourceLogIDs.
Connection is opened with autocommit=True per the controller revision:
usp_SyncApply manages its own transaction internally (BEGIN/ROLLBACK),
and an outer pyodbc transaction would conflict on ROLLBACK (SQL error
266). The dedup IF NOT EXISTS...INSERT is a single atomic statement.
Integration test self-cleans via SourceFile='sqlw_test.accdb' marker;
conn_str comes from the gitignored config.yaml (no hardcoded creds).
Co-Authored-By: Claude <noreply@anthropic.com>
