Week 5 Day 1: add provider telemetry contract

[utkarshp845]

Summary

• add a structured provider telemetry contract for optional LLM calls
• expose bounded provider/model identity, attempt state, outcome, latency, fallback, and normalized token usage
• keep prompts, evidence, credentials, provider URLs, generated output, and customer identifiers out of telemetry
• add success, failure, unconfigured fallback, API integration, latency, usage, and privacy tests
• document the Day 1 contract and restore the Weeks 5-8 technical roadmap alongside commercialization gates

Validation

• assistant tests: 25 passed
• demo-service tests: 6 passed
• Ruff: passed
• assistant evaluations: 7/7 cases and 35/35 checks passed
• git diff --check: passed

Scope boundary

This PR establishes per-request telemetry. Aggregate metrics, pricing inputs, cost estimation, cost per successful evaluated analysis, and provider comparison reporting remain later Week 5 work.