feat: mount store rw for main agent and add requiresTrigger to register_group

- Mount store/ separately as read-write so the main agent can access
  the SQLite database directly.
- Add requiresTrigger parameter to the register_group MCP tool
  (host IPC already supported it, but the tool never exposed it).
  Defaults to false (no trigger).
- Update group registration instructions to ask user about trigger.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/container-runner.ts

@@ -68,7 +68,7 @@ function buildVolumeMounts(
 
   if (isMain) {
     // Main gets the project root read-only. Writable paths the agent needs
-    // (group folder, IPC, .claude/) are mounted separately below.
+    // (store, group folder, IPC, .claude/) are mounted separately below.
     // Read-only prevents the agent from modifying host application code
     // (src/, dist/, package.json, etc.) which would bypass the sandbox
     // entirely on next restart.
@@ -89,6 +89,15 @@ function buildVolumeMounts(
       });
     }
 
+    // Main gets writable access to the store (SQLite DB) so it can
+    // query and write to the database directly.
+    const storeDir = path.join(projectRoot, 'store');
+    mounts.push({
+      hostPath: storeDir,
+      containerPath: '/workspace/project/store',
+      readonly: false,
+    });
+
     // Main also gets its group folder as the working directory
     mounts.push({
       hostPath: groupDir,