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.

tests/topology/test_repository_protocol.py

@@ -0,0 +1,21 @@
+"""Verify BaseRepository structurally satisfies TopologyRepository."""
+
+_PROTOCOL_METHODS = {
+    "create_topology",
+    "get_topology",
+    "update_topology_status",
+    "list_topologies",
+    "add_lan",
+    "list_lans_for_topology",
+    "add_topology_decky",
+    "list_topology_deckies",
+    "add_topology_edge",
+    "list_topology_edges",
+}
+
+
+def test_base_repository_satisfies_protocol() -> None:
+    from decnet.web.db.repository import BaseRepository
+
+    for name in _PROTOCOL_METHODS:
+        assert hasattr(BaseRepository, name), f"BaseRepository missing {name!r}"