[Documentation] Document implementation roadmap

[ConnorQi01]

Summary

Add a consolidated implementation roadmap for iOS-Automation-Framework.

Proposed Changes

• Merge the previous optimization and Web UI planning notes into one maintained document under docs/.
• Record which planned items are already complete, partially complete, or still pending based on the current upstream implementation.
• Preserve Web UI, test execution, safety, AI, and platform integration principles.
• Split remaining work into near-, mid-, and long-term guidance.

Test Plan

• Documentation-only change; no runtime tests required.

Closes #31