refactor: Reorganize src/ into modular folder structure

Split large monolithic files into focused modules:
- cloudcode-client.js (1,107 lines) → src/cloudcode/ (9 files)
- account-manager.js (639 lines) → src/account-manager/ (5 files)
- Move auth files to src/auth/ (oauth, token-extractor, database)
- Move CLI to src/cli/accounts.js

Update all import paths and documentation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/cloudcode/index.js

@@ -0,0 +1,28 @@
+/**
+ * Cloud Code Client for Antigravity
+ *
+ * Communicates with Google's Cloud Code internal API using the
+ * v1internal:streamGenerateContent endpoint with proper request wrapping.
+ *
+ * Supports multi-account load balancing with automatic failover.
+ *
+ * Based on: https://github.com/NoeFabris/opencode-antigravity-auth
+ */
+
+// Re-export public API
+export { sendMessage } from './message-handler.js';
+export { sendMessageStream } from './streaming-handler.js';
+export { listModels, fetchAvailableModels, getModelQuotas } from './model-api.js';
+
+// Default export for backwards compatibility
+import { sendMessage } from './message-handler.js';
+import { sendMessageStream } from './streaming-handler.js';
+import { listModels, fetchAvailableModels, getModelQuotas } from './model-api.js';
+
+export default {
+    sendMessage,
+    sendMessageStream,
+    listModels,
+    fetchAvailableModels,
+    getModelQuotas
+};