P0: workspace scaffold, CI gates, tc-domain, tc-config, tc-db vs real Postgres

- Cargo workspace with 1250-line and no-placeholder CI gates wired first
- tc-domain: id newtypes, SessionKey codec (proptest round-trip), Role,
  GatedCategory (spec §15), AccessPolicy, core entities
- tc-config: figment TOML+env config, DeployTarget/provider/auth selection
  with semantic validation
- migrations/0001: full spec §14 schema incl. DB-enforced append-only audit_log
- tc-db: compile-time-checked sqlx repos (workspaces, users, agents+policies,
  credits, audit) with committed .sqlx offline metadata
- tc-testkit: per-test real-Postgres databases (testcontainers or
  TC_TEST_DATABASE_URL), embedded migrations

Co-Authored-By: Claude Fable 5 <[email protected]>

.sqlx/query-f899f45e5d7a01a2a5ac868e33dddab7dbb8650de76cc4087c3e38338492a4bd.json

@@ -0,0 +1,28 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "INSERT INTO audit_log\n            (workspace_id, actor_kind, actor_id, event_type, subject_type,\n             subject_id, detail)\n         VALUES ($1, $2, $3, $4, $5, $6, $7)\n         RETURNING id",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Int8"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Uuid",
+        "Text",
+        "Uuid",
+        "Text",
+        "Text",
+        "Text",
+        "Jsonb"
+      ]
+    },
+    "nullable": [
+      false
+    ]
+  },
+  "hash": "f899f45e5d7a01a2a5ac868e33dddab7dbb8650de76cc4087c3e38338492a4bd"
+}