feat: add dashboard home page with collection cards, stats, and model metadata

[aGallea]

Summary

• New dashboard home page at / replacing the old Collections page — shows stats bar (collection count + total items), responsive collection cards grid with model metadata badges, and empty state onboarding
• Collection cards support Visualize (navigates to Plot), Inspect (inline metadata expand), and Delete (with confirmation) actions
• Backend enhancement: GET /api/collections now returns model_name and model_type from ChromaDB collection metadata
• Routing update: NavBar is now Home | Index | Plot; deleted CollectionsPage and CollectionList components

Changes

Area	Files	What
Backend	models.py, routes/collections.py	Added model_name/model_type to CollectionInfo, read from collection metadata
Frontend	HomePage.tsx, CollectionCard.tsx, CollectionGrid.tsx, StatsBar.tsx, EmptyState.tsx	New dashboard components
Frontend	App.tsx, types/index.ts	Updated routing and TypeScript types
Frontend	CollectionsPage.tsx, CollectionList.tsx	Deleted (replaced by HomePage + CollectionGrid)
Tests	test_server_collections.py	2 new tests for model metadata; updated assertions (8 total)

Test Plan

• 178 backend tests pass (98.54% coverage)
• ruff check + ruff format --check clean
• mypy strict mode clean
• Frontend tsc --noEmit + npm run build clean

[github-actions]

Tests Report 📄

Tests Succees ✅

JUnit Details

Total Tests	Failures	Errors	Skipped	Time ⏳
178	0	0	0	22.09s

Coverage Details (100% >= 90%) ✅

Diff Cover Details

File	Covered Lines		Missing Lines
embedding_cluster/server/models.py	2/2	100%
embedding_cluster/server/routes/collections.py	13/13	100%
Total	15/15	100%