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]>

crates/bins/teamclaw-server/src/main.rs

@@ -78,6 +78,8 @@ async fn run() -> Result<(), String> {
         RuntimeConfig {
             model: config.llm.model.clone(),
             max_tokens: 4096,
+            broker_socket: Some(PathBuf::from(&config.broker.socket_path)),
+            slack_base_url: config.slack.base_url.clone(),
         },
         blob,
     );
@@ -88,7 +90,12 @@ async fn run() -> Result<(), String> {
     tc_scheduler::Scheduler::new(pool.clone(), runtime.clone())
         .spawn(std::time::Duration::from_secs(5));
 
-    let app = tc_api::router(tc_api::AppState::new(pool, runtime));
+    let mut app = tc_api::router(
+        tc_api::AppState::new(pool, runtime).with_broker(PathBuf::from(&config.broker.socket_path)),
+    );
+    if e2e::enabled() {
+        app = app.merge(e2e::slack_sink_router());
+    }
     let listener = tokio::net::TcpListener::bind(config.listen_addr)
         .await
         .map_err(|e| format!("bind {} failed: {e}", config.listen_addr))?;