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>

convert_firmware_key.sh

@@ -79,17 +79,17 @@ key_bytes = bytes.fromhex(key_hex)
 # Verify with pyMC if available
 try:
     from nacl.bindings import crypto_scalarmult_ed25519_base_noclamp
-    
+
     scalar = key_bytes[:32]
     pubkey = crypto_scalarmult_ed25519_base_noclamp(scalar)
-    
+
     print(f"Derived public key: {pubkey.hex()}")
-    
+
     # Calculate address (MeshCore uses first byte of pubkey directly, not SHA256)
     address = pubkey[0]
     print(f"Node address: 0x{address:02x}")
     print()
-    
+
 except ImportError:
     print("Warning: PyNaCl not available, skipping verification")
     print()