docs: add Phase 3 UI information architecture

Comprehensive design for golden path web UI with 6 core views:
- Workspace View: Overview & initialization
- PRD View: Document creation & Socratic discovery
- Task Board View: Kanban & batch execution
- Execution Monitor View: Real-time SSE streaming
- Blocker Resolution View: Answer agent questions
- Review & Commit View: Diff viewer & git actions

Includes:
- Component hierarchies for each view
- Navigation structure and URL routing
- Real-time patterns (SSE event handling)
- Interaction patterns (discovery flow, batch execution)
- Anti-patterns to avoid (feature creep, over-engineering)

Issues created: #329-#334

Author: Test User