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/service_utils.py

@@ -2,6 +2,7 @@
 Service management utilities for pyMC Repeater.
 Provides functions for service control operations like restart.
 """
+
 import logging
 import subprocess
 from typing import Tuple
@@ -21,12 +22,9 @@ def restart_service() -> Tuple[bool, str]:
     """
     try:
         result = subprocess.run(
-            ['systemctl', 'restart', 'pymc-repeater'],
-            capture_output=True,
-            text=True,
-            timeout=5
+            ["systemctl", "restart", "pymc-repeater"], capture_output=True, text=True, timeout=5
         )
-        
+
         if result.returncode == 0:
             logger.info("Service restart command executed successfully")
             return True, "Service restart initiated"