Allow NULL workflow_id in executions table for quick commands

Changes:
- Modified executions table schema to allow NULL workflow_id
- Removed foreign key constraint that prevented NULL values
- Added migration to update existing table structure
- Quick commands can now be stored without a workflow reference

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

server.js

@@ -75,19 +75,33 @@ async function initDatabase() {
     await connection.query(`
       CREATE TABLE IF NOT EXISTS executions (
         id VARCHAR(36) PRIMARY KEY,
-        workflow_id VARCHAR(36) NOT NULL,
+        workflow_id VARCHAR(36) NULL,
         status VARCHAR(50) NOT NULL,
         started_by VARCHAR(255),
         started_at TIMESTAMP NULL,
         completed_at TIMESTAMP NULL,
         logs JSON,
-        FOREIGN KEY (workflow_id) REFERENCES workflows(id) ON DELETE CASCADE,
         INDEX idx_workflow (workflow_id),
         INDEX idx_status (status),
         INDEX idx_started (started_at)
       )
     `);
 
+    // Migrate existing executions table to allow NULL workflow_id
+    try {
+      await connection.query(`
+        ALTER TABLE executions
+        MODIFY workflow_id VARCHAR(36) NULL,
+        DROP FOREIGN KEY executions_ibfk_1
+      `);
+      console.log('Executions table migrated to allow NULL workflow_id');
+    } catch (error) {
+      // Ignore error if foreign key doesn't exist or already modified
+      if (!error.message.includes('check that column/key exists')) {
+        console.log('Migration note:', error.message);
+      }
+    }
+
     console.log('Database tables initialized successfully');
   } catch (error) {
     console.error('Database initialization error:', error);