feat(topology): persist comparison runs + history

Save each comparison and let users reload past ones.
- migration 0008: topology_runs (workspace-scoped; full comparison as JSONB).
- cm-db repo::topology_runs (insert / list_recent / get) + regenerated .sqlx.
- cm-api: compare persists best-effort (never loses the LLM result on a DB
  hiccup); GET /api/topology-runs (recent) + GET /api/topology-runs/{id}.
  Integration test asserts persist → list → get.
- frontend: "Recent comparisons" list on the Compare tab; click to reload a
  saved run. e2e p8 green (39 suite); offline build + clippy clean.

Server self-migrates at boot (cm_db::MIGRATOR), so 0008 applies on deploy.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

.sqlx/query-d0af8ed0859959bf080a23068c3fce9fd80c6a0646010d8682b9f37706ffdd00.json

@@ -0,0 +1,17 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "INSERT INTO topology_runs (id, workspace_id, task, comparison)\n         VALUES ($1, $2, $3, $4)",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Uuid",
+        "Uuid",
+        "Text",
+        "Jsonb"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "d0af8ed0859959bf080a23068c3fce9fd80c6a0646010d8682b9f37706ffdd00"
+}