feat: add traceback-driven ecommerce repair demo platform

[xubinrui]

Summary

• add an independent ecommerce microservice stack under ecommerce-platform for traceback-driven repair demos
• add structured service and gateway logging, live monitor UI, traffic replay, hot reload scripts, and realistic fault injection paths
• add reproducible million-scale log dataset generation and document ignored log directory rules plus regeneration commands

Included Commits

• feat(ecom): add structured service event logging
• feat(ecom): add local gateway monitor and log replay
• feat(ecom): add realistic traceback bug scenarios
• feat(ecom): add local hot reload stack scripts
• feat(ecom): add reproducible log dataset generation

Verification

• cd ecommerce-platform && .venv/bin/pytest
• validated the local reload stack, monitor endpoint, and live traffic simulator manually