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/db/models/topology.py

@@ -237,6 +237,8 @@ class TopologySummary(BaseModel):
     needs_resync: bool = False
     created_at: datetime
     status_changed_at: Optional[datetime] = None
+    email_personas: str = "[]"
+    language_default: str = "en"
 
 
 class TopologyListResponse(BaseModel):