feat(#131): add OpenTelemetry tracing infrastructure

Implement comprehensive distributed tracing for HTTP requests and LLM
operations using OpenTelemetry with GenAI semantic conventions.

Features:
- TelemetryService: SDK initialization with OTLP HTTP exporter
- TelemetryInterceptor: Automatic HTTP request spans
- @TraceLlmCall decorator: LLM operation tracing
- GenAI semantic conventions for model/token tracking
- Graceful degradation when tracing disabled

Instrumented:
- All HTTP requests (automatic spans)
- OllamaProvider chat/chatStream/embed operations
- Token counts, model names, durations

Environment:
- OTEL_ENABLED (default: true)
- OTEL_SERVICE_NAME (default: mosaic-api)
- OTEL_EXPORTER_OTLP_ENDPOINT (default: localhost:4318)

Tests: 23 passing with full coverage

Fixes #131

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

apps/api/src/telemetry/index.ts

@@ -0,0 +1,17 @@
+/**
+ * OpenTelemetry distributed tracing module.
+ * Provides HTTP request tracing and LLM operation instrumentation.
+ *
+ * @module telemetry
+ */
+
+export { TelemetryModule } from "./telemetry.module";
+export { TelemetryService } from "./telemetry.service";
+export { TelemetryInterceptor } from "./telemetry.interceptor";
+export { SpanContextService } from "./span-context.service";
+export {
+  TraceLlmCall,
+  createLlmSpan,
+  recordLlmUsage,
+  type LlmTraceMetadata,
+} from "./llm-telemetry.decorator";