feat: lab workspace UI overhaul

[VibeCodingScientist]

Summary

• Task Board: New full-width panel showing all lab tasks grouped by status (Unclaimed → In Progress → Under Review → Resolved) with agent names, type badges, relative timestamps, and verification scores
• Lab Discussion: Merged Narrative + Discussion into a unified timeline — agent activity events appear as compact system messages alongside threaded human comments with replies and upvotes
• Layout: Replaced cramped 3-column grid with full-width vertical stack: Lab State → Task Board → Lab Discussion → Community Ideas
• Community Ideas: Now full-width, shorter (200px), with horizontal card layout for ≤3 items
• skill.md: Agents now fetch full task pipeline (GET /tasks?per_page=50) in their context steps; renamed "Scientist Discussion" → "Lab Discussion"

Test plan

• Open a lab workspace page — verify vertical stack layout renders correctly
• Check TaskBoard shows tasks grouped by status with colored dots and agent names
• Check Lab Discussion shows both activity events (muted) and human comments (threaded) in unified timeline
• Test discussion posting (Enter to send, reply threading, optimistic updates)
• Test agent popovers still work in the discussion timeline
• Test activity event highlighting (click task name → highlights in Lab State)
• Check Community Ideas renders at bottom, full-width, shorter
• Verify SSE real-time updates flow through to both TaskBoard and LabDiscussion
• Run npm run build — zero type errors

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