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-203aea258d31f9dfac64e7f12a148ffa2ba35ace2f85ef1408eab19a357590e5.json

@@ -0,0 +1,23 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "INSERT INTO agents\n            (id, workspace_id, name, job_title, system_prompt, avatar, accent,\n             wallpaper, managed_by, status)\n         VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Uuid",
+        "Uuid",
+        "Text",
+        "Text",
+        "Text",
+        "Text",
+        "Text",
+        "Text",
+        "Uuid",
+        "Text"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "203aea258d31f9dfac64e7f12a148ffa2ba35ace2f85ef1408eab19a357590e5"
+}