fix(ws2): register /new-task slash command + commands scope in Slack manifest

The slack_listener handles {type:slash_commands, command:/new-task} but the app
manifest declared no slash commands and no 'commands' scope, so Slack never
offered /new-task (the command can't be invoked). Add the slash command +
commands bot scope. Socket Mode delivers it over the socket (no request URL).
APPLY: update the app A0BCC7TTU66 from this manifest + reinstall to pick up the
new scope.

agent-team/slack/agent-team-manifest.json

@@ -8,7 +8,15 @@
     "bot_user": {
       "display_name": "agent-team",
       "always_online": true
-    }
+    },
+    "slash_commands": [
+      {
+        "command": "/new-task",
+        "description": "Start a new agent-team task (clarify -> plan -> review)",
+        "usage_hint": "<task description>",
+        "should_escape": false
+      }
+    ]
   },
   "oauth_config": {
     "scopes": {
@@ -17,7 +25,8 @@
         "channels:history",
         "groups:history",
         "im:history",
-        "app_mentions:read"
+        "app_mentions:read",
+        "commands"
       ]
     }
   },