feat(plot): add multi-select point emphasis in cluster drawer

[aGallea]

Summary

• add multi-select point selection from the cluster drawer with clear/select-page controls and expanded selected rows
• emphasize selected products across particle, sphere, and sprite renderers so chosen items remain visible in the plot
• add selected-product distance comparison rows in the drawer and extend Playwright coverage for the new flow

Verification

• npm run build
• npm run test:e2e -- e2e/cluster-drawer.spec.ts --workers=1
• npm run test:e2e -- e2e/tooltip-positioning.spec.ts
• npm run test:e2e -- e2e/search.spec.ts -g "hovering points does not trigger visualization error"

[github-actions]

Tests Report 📄

Tests Succees ✅

JUnit Details

Total Tests	Failures	Errors	Skipped	Time ⏳
242	0	0	0	62.45s

Coverage Details (100% >= 90%) ✅

Diff Cover Details

File	Covered Lines		Missing Lines
embedding_cluster/annotations.py	69/69	100%
embedding_cluster/scatter_plot.py	3/3	100%
embedding_cluster/server/app.py	4/4	100%
embedding_cluster/server/models.py	67/67	100%
embedding_cluster/server/routes/annotations.py	57/57	100%
embedding_cluster/server/routes/plot.py	185/186	99%	250
Total	385/386	100%