feat(#52): implement Active Projects & Agent Chains widget

Add HUD widget for tracking active projects and running agent sessions.

Backend:
- Add getActiveProjectsData() and getAgentChainsData() to WidgetDataService
- Create POST /api/widgets/data/active-projects endpoint
- Create POST /api/widgets/data/agent-chains endpoint
- Add WidgetProjectItem and WidgetAgentSessionItem response types

Frontend:
- Create ActiveProjectsWidget component with dual panels
- Active Projects panel: name, color, task/event counts, last activity
- Agent Chains panel: status, runtime, message count, expandable details
- Real-time updates (projects: 30s, agents: 10s)
- PDA-friendly status indicators (Running vs URGENT)

Testing:
- 7 comprehensive tests covering loading, rendering, empty states, expandability
- All tests passing (7/7)

Refs #52

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docs/reports/qa-automation/pending/home-jwoltje-src-mosaic-stack-apps-web-src-components-widgets-ActiveProjectsWidget.tsx_20260203-1917_1_remediation_needed.md

@@ -0,0 +1,20 @@
+# QA Remediation Report
+
+**File:** /home/jwoltje/src/mosaic-stack/apps/web/src/components/widgets/ActiveProjectsWidget.tsx
+**Tool Used:** Write
+**Epic:** general
+**Iteration:** 1
+**Generated:** 2026-02-03 19:17:02
+
+## Status
+
+Pending QA validation
+
+## Next Steps
+
+This report was created by the QA automation hook.
+To process this report, run:
+
+```bash
+claude -p "Use Task tool to launch universal-qa-agent for report: /home/jwoltje/src/mosaic-stack/docs/reports/qa-automation/pending/home-jwoltje-src-mosaic-stack-apps-web-src-components-widgets-ActiveProjectsWidget.tsx_20260203-1917_1_remediation_needed.md"
+```