feat: add overview dashboard, background pipeline execution, and shared

[swati510]

persistence layer

• Add repository overview page with health score ring, attention panel, language donut, ownership treemap, hotspots mini, decisions timeline, module minimap, quick actions, and active job banner
• Extract persist_pipeline_result() into core/pipeline/persist.py so both CLI and server share the same persistence logic
• Add server job_executor that runs the full pipeline in the background via asyncio.create_task, with batched progress writes and drain logic
• Make sync/full-resync endpoints launch background jobs with concurrent run prevention (HTTP 409)
• Reset stale running jobs on server startup (crash recovery)
• Improve pipeline orchestrator async behavior (wrap_future, to_thread, periodic sleep(0) yields)
• Update docs: ARCHITECTURE.md, CHANGELOG.md, USER_GUIDE.md, QUICKSTART.md

Summary

feat: add overview dashboard, background pipeline execution, and shared
persistence layer

• Add repository overview page with health score ring, attention panel,
  language donut, ownership treemap, hotspots mini, decisions timeline,
  module minimap, quick actions, and active job banner

• Extract persist_pipeline_result() into core/pipeline/persist.py so
  both CLI and server share the same persistence logic

• Add server job_executor that runs the full pipeline in the background
  via asyncio.create_task, with batched progress writes and drain logic

• Make sync/full-resync endpoints launch background jobs with concurrent
  run prevention (HTTP 409)

• Reset stale running jobs on server startup (crash recovery)

• Improve pipeline orchestrator async behavior (wrap_future, to_thread,
  periodic sleep(0) yields)

• Update docs: ARCHITECTURE.md, CHANGELOG.md, USER_GUIDE.md,
  QUICKSTART.md

Related Issues

Test Plan

• [x ] Tests pass (pytest)
• [ x] Lint passes (ruff check .)
• [ x] Web build passes (npm run build) (if frontend changes)

Checklist

• [x ] My code follows the project's code style
• [x ] I have added tests for new functionality
• [x ] All existing tests still pass
• [x ] I have updated documentation if needed