Add Module 1: Observability Primitives & Instrumentation

[gwho]

Implement comprehensive FastAPI + Logfire observability lab with:

Phase 1 - Service Skeleton:

• Initialize FastAPI application with auto-instrumentation
• Configure Logfire with service name 'observability-lab-01'
• Apply logfire.instrument_fastapi(app) hook for automatic tracing
• Add fallback console-only mode for local development

Phase 2 - Structural Depth:

• Implement GET /process-order/{order_id} endpoint
• Use structured logging (key-value pairs) instead of string formatting
• Create manual 'verify_inventory' span for granular tracing
• Simulate database latency with random sleep (0.1s-0.5s)
• Log warnings for slow queries (>0.4s threshold)
• Attach metadata to spans for queryability

Phase 3 - Verification Challenge:

• Add conditional error injection for order_id='error-test'
• Raise HTTPException with 500 status code
• Provide structured error logging with context
• Enable full exception trace correlation

Testing & Verification:

• All endpoints tested and verified working
• Regular order processing with timing information
• Slow query detection and warning logging
• Error case with proper exception handling
• Comprehensive test results documented

Documentation:

• Complete README with setup instructions
• Detailed implementation guide
• Testing and verification procedures
• TEST_RESULTS.md with actual test outputs
• Logfire dashboard usage instructions

This implementation demonstrates production-ready observability
practices suitable for real-world applications.