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/telemetry.module.ts

@@ -0,0 +1,23 @@
+import { Module, Global } from "@nestjs/common";
+import { TelemetryService } from "./telemetry.service";
+import { TelemetryInterceptor } from "./telemetry.interceptor";
+import { SpanContextService } from "./span-context.service";
+
+/**
+ * Global module providing OpenTelemetry distributed tracing.
+ * Automatically instruments HTTP requests and provides utilities for LLM tracing.
+ *
+ * @example
+ * ```typescript
+ * @Module({
+ *   imports: [TelemetryModule],
+ * })
+ * export class AppModule {}
+ * ```
+ */
+@Global()
+@Module({
+  providers: [TelemetryService, TelemetryInterceptor, SpanContextService],
+  exports: [TelemetryService, TelemetryInterceptor, SpanContextService],
+})
+export class TelemetryModule {}