refactor: companion FrameServer and related (substantive only, no Black)

Reapply refactor from ce8381a (replace monolithic FrameServer with thin
pymc_core subclass, re-export constants, SQLite persistence hooks) while
preserving pre-refactor whitespace where patch applied cleanly. Remaining
files match refactor commit exactly. Diff vs ce8381a is whitespace-only.

Co-authored-by: Cursor <cursoragent@cursor.com>

repeater/data_acquisition/storage_utils.py

@@ -1,6 +1,6 @@
 """Storage utility classes and functions for data acquisition."""
 
-from dataclasses import dataclass, asdict
+from dataclasses import asdict, dataclass
 from datetime import datetime
 from typing import Optional