Critical Frontend Refactoring - Break up monolithic app.html

[laserpointlabs]

Problem: frontend/app.html is 31,522 lines with all UI, workbenches, and JavaScript making plugin migration impossible.

Solution: Refactor into modular structure:

• Create js/core/ for initialization and state management
• Create js/components/ for toolbar and panel management
• Create js/workbenches/ modular per workbench
• Extract DAS module to js/das/
• Create centralized API client
• Update index.html to load modular JavaScript

Priority: CRITICAL BLOCKER - Must complete before plugin system

Related: Plugin architecture plan, Issue 52

[laserpointlabs]

Part of Incremental Refactoring Epic (#71) - Phase 2 completion