P4 core: broker-held app connections + gated, broker-executed Slack posting

- app_connections repo; POST /api/apps/connect (keys/basic): the credential
  goes to the secret broker over its socket and only the encrypted ref lands
  in the row; disconnect endpoint; /api/apps directory merged with live
  connection status; audit rows for connect/disconnect
- Broker protocol: InvokeHttp carries a JSON body
- slack.post tool (SendsExternally -> gated): marked broker_executed — the
  runtime skips its own grant consumption and the BROKER independently
  verifies + consumes the single-use grant, then calls Slack with the bot
  token injected; the runtime never sees the credential
- Config: [broker] socket_path + [slack] base_url; e2e harness spawns the
  real teamclaw-broker daemon and the server hosts an e2e-only /__slack sink
- SlackApp: Connection tab stores the token via the broker; connected state
- Integration test: blocked while pending -> approved -> sink received
  exactly one post with 'Bearer xoxb-test-token' -> grant replay refused
- E2E journey: connect Slack in the panel -> gated post card with preview ->
  sink empty while pending -> approve -> exactly one post, queue clear

133 Rust + 63 frontend tests + 21 Playwright journeys.

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

.sqlx/query-fac227a443035c5f5acd5e09bdb64aea38509b2c3ae2b9d5dd3768dc609578b7.json

@@ -0,0 +1,60 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "SELECT id, workspace_id, agent_id, provider, auth_type, status, secret_ref\n           FROM app_connections\n           WHERE workspace_id = $1 AND (agent_id IS NULL OR agent_id = $2)\n             AND provider = $3 AND status = 'connected'\n           ORDER BY created_at DESC LIMIT 1",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Uuid"
+      },
+      {
+        "ordinal": 1,
+        "name": "workspace_id",
+        "type_info": "Uuid"
+      },
+      {
+        "ordinal": 2,
+        "name": "agent_id",
+        "type_info": "Uuid"
+      },
+      {
+        "ordinal": 3,
+        "name": "provider",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 4,
+        "name": "auth_type",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 5,
+        "name": "status",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 6,
+        "name": "secret_ref",
+        "type_info": "Uuid"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Uuid",
+        "Uuid",
+        "Text"
+      ]
+    },
+    "nullable": [
+      false,
+      false,
+      true,
+      false,
+      false,
+      false,
+      true
+    ]
+  },
+  "hash": "fac227a443035c5f5acd5e09bdb64aea38509b2c3ae2b9d5dd3768dc609578b7"
+}