feat(#125): add Claude (Anthropic) LLM provider

Implement Anthropic Claude provider for Claude Opus, Sonnet, and Haiku models.

Implementation details:
- Created ClaudeProvider class implementing LlmProviderInterface
- Added @anthropic-ai/sdk npm package integration
- Implemented chat completion with streaming support
- Claude-specific message format (system prompt separate from messages)
- Static model list (Claude API doesn't provide list models endpoint)
- Embeddings throw error as Claude doesn't support native embeddings
- Added OpenTelemetry tracing with @TraceLlmCall decorator
- 100% statement, function, and line coverage (79% branch coverage)

Tests:
- Created comprehensive test suite with 20 tests
- All tests follow TDD pattern (written before implementation)
- Tests cover initialization, health checks, chat, streaming, and error handling
- Mocked Anthropic SDK client for isolated unit testing

Quality checks:
- All tests pass (1131 total tests across project)
- ESLint passes with no errors
- TypeScript type checking passes
- Follows existing code patterns from OpenAI and Ollama providers

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/package.json

@@ -24,6 +24,7 @@
     "prisma:reset": "prisma migrate reset"
   },
   "dependencies": {
+    "@anthropic-ai/sdk": "^0.72.1",
     "@mosaic/shared": "workspace:*",
     "@nestjs/common": "^11.1.12",
     "@nestjs/core": "^11.1.12",