feat: AI cluster naming with LiteLLM multi-provider support

[aGallea]

Summary

Replace the old GPT-specific cluster naming with a provider-agnostic AI naming system powered by LiteLLM (100+ LLM providers).

• LiteLLM integration: Replaced openai dependency with litellm for universal LLM access (OpenAI, Anthropic, Gemini, Ollama, etc.)
• Settings page: New /settings route for configuring AI provider, model, API key, base URL, and temperature. Settings stored in browser localStorage; API key sent per-request (never persisted server-side)
• On-demand top-level naming: "Name with AI" button in the cluster legend calls /api/ai/name-clusters and saves results as annotations
• Automatic sub-cluster naming: Sub-clusters are automatically named via AI when computed, with parent cluster name as context in the prompt
• Backend endpoints: Three new API routes (/api/ai/name-clusters, /api/ai/name-sub-clusters, /api/ai/test-connection) with full test coverage

Changes

Backend (Python)

• Replace openai with litellm in pyproject.toml
• Remove GPT fields from Settings, PlotRequest, and scatter plot code
• New ai_naming.py module with get_cluster_name(), get_sub_cluster_name(), test_connection()
• New routes/ai.py with three endpoints and sample-based item extraction
• Add AI Pydantic models to models.py
• 9 tests for ai_naming, 12 tests for AI routes (265 total, all passing, 97%+ coverage)

Frontend (TypeScript/React)

• New SettingsPage.tsx with full AI configuration form and connection test
• New api/ai.ts with localStorage management and API client functions
• "Name with AI" button in ClusterLegend.tsx for top-level clusters
• Auto-naming integration in ClusterDetailDrawer.tsx for sub-clusters
• plotStore.ts additions: isNamingClusters, isNamingSubClusters, updateSubClusterNames
• Removed all GPT-specific UI from PlotControls.tsx
• Updated types in types/index.ts

Verification

• TypeScript: npx tsc --noEmit clean
• Backend: 265 tests passing, mypy strict clean on all 21 source files
• Pre-commit hooks: All passing

[github-actions]

Tests Report 📄

Tests Succees ✅

JUnit Details

Total Tests	Failures	Errors	Skipped	Time ⏳
265	0	0	0	64.09s

Coverage Details (100% >= 90%) ✅

Diff Cover Details

File	Covered Lines		Missing Lines
embedding_cluster/ai_naming.py	111/111	100%
embedding_cluster/scatter_plot.py	4/4	100%
embedding_cluster/server/app.py	2/2	100%
embedding_cluster/server/models.py	36/36	100%
embedding_cluster/server/routes/ai.py	159/160	99%	98
Total	312/313	100%