feat: Implement CLI session-based Full Stack mode

Replaces WebContainer-based approach with simpler Claude Code CLI session
shell command execution. This eliminates COOP/COEP header requirements
and reduces bundle size by ~350KB.

Changes:
- Added executeShellCommand() to ClaudeService for spawning bash processes
- Added /claude/api/shell-command API endpoint for executing commands
- Updated Full Stack mode (chat-functions.js) to use CLI sessions
- Simplified terminal mode by removing WebContainer dependencies

Benefits:
- No SharedArrayBuffer/COOP/COEP issues
- Uses existing Claude Code infrastructure
- Faster startup, more reliable execution
- Better error handling and output capture

Fixes:
- Terminal creation failure in Full Stack mode
- WebContainer SharedArrayBuffer serialization errors

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

services/claude-service.js

@@ -59,6 +59,88 @@ class ClaudeCodeService extends EventEmitter {
     return session;
   }
 
+  /**
+   * Execute shell command in session (for Full Stack mode)
+   * Spawns a shell process, sends command, captures output
+   */
+  async executeShellCommand(sessionId, command) {
+    const session = this.sessions.get(sessionId);
+
+    if (!session) {
+      throw new Error(`Session ${sessionId} not found`);
+    }
+
+    if (session.status !== 'running') {
+      throw new Error(`Session ${sessionId} is not running`);
+    }
+
+    console.log(`[ClaudeService] Executing shell command in ${sessionId}:`, command);
+
+    // Spawn shell to execute the command
+    const shell = spawn('bash', ['-c', command], {
+      cwd: session.workingDir,
+      stdio: ['ignore', 'pipe', 'pipe'],
+      env: {
+        ...process.env,
+        TERM: 'xterm-256color'
+      }
+    });
+
+    let stdout = '';
+    let stderr = '';
+
+    shell.stdout.on('data', (data) => {
+      const text = data.toString();
+      stdout += text;
+
+      // Add to output buffer
+      session.outputBuffer.push({
+        type: 'shell',
+        timestamp: new Date().toISOString(),
+        content: text
+      });
+
+      // Emit for real-time updates
+      this.emit('session-output', {
+        sessionId,
+        type: 'stdout',
+        content: text
+      });
+    });
+
+    shell.stderr.on('data', (data) => {
+      const text = data.toString();
+      stderr += text;
+
+      session.outputBuffer.push({
+        type: 'stderr',
+        timestamp: new Date().toISOString(),
+        content: text
+      });
+
+      this.emit('session-output', {
+        sessionId,
+        type: 'stderr',
+        content: text
+      });
+    });
+
+    return new Promise((resolve) => {
+      shell.on('close', (code) => {
+        const exitCode = code !== null ? code : -1;
+
+        console.log(`[ClaudeService] Shell command completed with exit code ${exitCode}`);
+
+        resolve({
+          exitCode,
+          stdout,
+          stderr,
+          success: exitCode === 0
+        });
+      });
+    });
+  }
+
   /**
    * Send command to a session using -p (print) mode
    */
@@ -94,6 +176,14 @@ class ClaudeCodeService extends EventEmitter {
       timestamp: new Date().toISOString()
     });
 
+    // Also save user message to outputBuffer for persistence
+    session.outputBuffer.push({
+      type: 'user',
+      role: 'user',
+      timestamp: new Date().toISOString(),
+      content: command
+    });
+
     session.lastActivity = new Date().toISOString();
 
     this.emit('command-sent', {