Replaces the subprocess call to mempalace CLI binary with direct SovereignStore import. L1 palace search now uses SQLite + FTS5 + HRR vectors in-process. No ONNX, no subprocess, no API calls.
Removes: import subprocess, MEMPALACE_BIN constant
Adds: SovereignStore lazy singleton, _get_store(), SOVEREIGN_DB path
Closes#383
Depends on #380 (sovereign_store.py)