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/topology/allocator.py

@@ -14,8 +14,8 @@ from __future__ import annotations
 from ipaddress import IPv4Network
 from typing import Iterable
 
+from decnet.topology.repository import TopologyRepository
 from decnet.topology.status import TopologyStatus
-from decnet.web.db.repository import BaseRepository
 
 
 class AllocatorExhausted(RuntimeError):
@@ -150,13 +150,12 @@ _SUBNET_CLAIMING_STATES: frozenset[str] = frozenset(
 )
 
 
-async def reserved_subnets(repo: BaseRepository) -> set[str]:
+async def reserved_subnets(repo: TopologyRepository) -> set[str]:
     """All LAN subnets currently claimed by non-torn-down topologies."""
     out: set[str] = set()
     for status in _SUBNET_CLAIMING_STATES:
         for topo in await repo.list_topologies(status=status):
-            for lan in await repo.list_lans_for_topology(topo["id"]):
-                subnet = lan.get("subnet")
-                if subnet:
-                    out.add(subnet)
+            for lan in await repo.list_lans_for_topology(topo.id):
+                if lan.subnet:
+                    out.add(lan.subnet)
     return out