refactor(topology): introduce TopologyRepository protocol with DTO return types

Replace repo: BaseRepository with a structural TopologyRepository protocol
in persistence.py and allocator.py. All read methods now return typed DTOs
(TopologySummary, LANRow, DeckyRow, EdgeRow) instead of raw dicts, eliminating
silent field-shape regressions across the topology subsystem.

TopologySummary gains email_personas and language_default so api_personas.py
can continue reading those fields via attribute access. hydrate() converts
DTOs to dicts before passing to _backfill_decky_configs, keeping the mutable
working-state function dict-based at its boundary. All production callers
(router handlers, mutator, CLI, heartbeat) migrated from dict/get access to
attribute access. 134 tests pass.

decnet/mutator/engine.py

@@ -284,13 +284,13 @@ async def reconcile_agent_resyncs(repo: BaseRepository) -> int:
         return 0
     drained = 0
     for topo in pending:
-        tid = topo["id"]
+        tid = topo.id
         try:
             await _deployer.resync_agent_topology(repo, tid)
             await repo.set_topology_resync(tid, False)
             drained += 1
             log.info("topology %s resynced to agent %s",
-                     tid, topo.get("target_host_uuid"))
+                     tid, topo.target_host_uuid)
         except Exception as exc:  # noqa: BLE001
             log.warning(
                 "topology %s resync failed (will retry): %s", tid, exc,