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/web/router/topology/api_events.py

@@ -69,7 +69,7 @@ async def api_topology_events(
     # GET /topologies/{id}/mutations). Adding a new event family here
     # requires a threat-model review for F6/I (role leakage).
     topo = await get_topology_or_404(topology_id)
-    snapshot_status = topo["status"]
+    snapshot_status = topo.status
     in_flight: list[dict] = []
     for state in _IN_FLIGHT_STATES:
         in_flight.extend(await repo.list_topology_mutations(topology_id, state=state))