Comprehensive documentation overhaul to match current SDK implementation

- Complete rewrite of API.md to document actual exported classes and functions - Added missing OAuth classes: GoogleDriveOAuth, DropboxOAuth with static methods - Added missing Selection classes: GoogleDriveSelection, DropboxSelection - Added base API functions: createSourceConnector, manageUser, getOneTimeConnectorToken - Updated types.md with missing GoogleDriveOAuthConfig and corrected interfaces - Fixed all function signatures to match actual source code implementations - Updated guide files to use class-based approach instead of non-existent functions - Ensured consistent VECTORIZE_TOKEN environment variable usage throughout - All documentation now accurately reflects the SDK's actual API surface Co-Authored-By: dikshant.pradhan@vectorize.io <dikshant.pradhan@vectorize.io>

Author: devin-ai-integration[bot]