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-b4f2ebe304fa3b4722584bfe6c3df389b46d52724fc9b137dbe83b3d4fce2983.json

@@ -0,0 +1,41 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "SELECT id, task, comparison, created_at FROM topology_runs\n         WHERE id = $1 AND workspace_id = $2",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Uuid"
+      },
+      {
+        "ordinal": 1,
+        "name": "task",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 2,
+        "name": "comparison",
+        "type_info": "Jsonb"
+      },
+      {
+        "ordinal": 3,
+        "name": "created_at",
+        "type_info": "Timestamptz"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Uuid",
+        "Uuid"
+      ]
+    },
+    "nullable": [
+      false,
+      false,
+      false,
+      false
+    ]
+  },
+  "hash": "b4f2ebe304fa3b4722584bfe6c3df389b46d52724fc9b137dbe83b3d4fce2983"
+}