FU-P11-T2-1: Push session data via WebSocket for real-time timeline updates

[SoundBlaster]

Description

Extends the WebSocket metrics_update message to include session data from detect_sessions(), so the session timeline refreshes in real-time on every WebSocket push instead of a 15-second poll.

Changes:

• server.py: adds sessions key to metrics_update WS payload (calls detect_sessions on each broadcast tick)
• dashboard.js: handleMetricsUpdate now calls renderTimeline(data.sessions) when present; HTTP fallback polling also includes sessions for the WS-disconnected case; setInterval(loadSessions, 15000) removed
• test_server.py: new test asserting WS message contains sessions list

Also fixes workplan ✅ marker formatting for P11-T1 and FU-P11-T2-1/2 dependency lines (pick_next_task.py parsing issue).

Closes FU-P11-T2-1. Validation report: SPECS/ARCHIVE/FU-P11-T2-1_Push_Session_Data_via_WebSocket/FU-P11-T2-1_Validation_Report.md

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactoring
• CI/CD improvement

Quality Gates

• make test - All tests pass with ≥90% coverage (458 passed, 95.95% coverage)
• make lint - No linting errors (ruff check src/ — All checks passed)
• make format - Code is properly formatted
• make typecheck - Type checking passes
• make doccheck - Documentation is synced with DocC (if docs changed)

Documentation Sync

• Documentation changes are synced with DocC catalog (or N/A)

Testing

• Added/updated tests for new functionality
• All tests pass locally
• Manually tested the changes

Checklist

• Code follows the project's style guidelines
• Self-review completed
• Comments added for complex code
• Documentation updated (if needed)
• No new warnings generated
• PR title is descriptive