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/handler_helpers/discovery.py

@@ -7,6 +7,7 @@ allowing other nodes to discover repeaters on the mesh network.
 
 import asyncio
 import logging
+
 from pymc_core.node.handlers.control import ControlHandler
 
 logger = logging.getLogger("DiscoveryHelper")