JSDoc annotations across all modules

[theonlytruebigmac]

Description

Add JSDoc annotations to all exported functions across all modules for better IDE support and auto-generated documentation.

Scope

• JSDoc comments for all public functions in scraper.js, storage.js, popup.js, service-worker.js
• Type annotations for parameters and return values
• Generate API docs from JSDoc (optional: use jsdoc or typedoc)

Acceptance Criteria

• All public functions have JSDoc with @param, @returns, @description
• IDE autocomplete works for all functions
• No JSDoc warnings or errors
• Types are accurate and helpful

Part of #5