Use org URL for cases API root

[maximelb]

Summary

• The Cases SDK now lazily resolves the cases service URL from the org URLs endpoint (org.get_urls()["cases"]) instead of hardcoding https://cases.limacharlie.io.
• This allows proper routing to staging environments for exp-1 datacenter orgs whose org URLs return a different cases endpoint.
• Explicit api_root parameter and LC_CASES_API_ROOT env var still take priority. Falls back to the hardcoded default if the org URL endpoint has no "cases" key or errors out.

Test plan

• Updated TestCasesInit with tests for org URL resolution, scheme handling, caching, and error fallback
• All 64 existing unit tests pass

🤖 Generated with Claude Code