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_mutations.py

@@ -63,11 +63,11 @@ async def api_enqueue_mutation(
     _admin: dict = Depends(require_admin),
 ) -> MutationEnqueueResponse:
     topo = await get_topology_or_404(topology_id)
-    if topo["status"] not in _MUTATABLE:
+    if topo.status not in _MUTATABLE:
         raise HTTPException(
             status_code=409,
             detail=(
-                f"Topology is {topo['status']!r}; the mutation queue is "
+                f"Topology is {topo.status!r}; the mutation queue is "
                 f"only open for 'active' or 'degraded' topologies.  Use "
                 f"child-CRUD endpoints while pending."
             ),