fix(docs): align quick-start OTLP port

[AnxForever]

What & why

Align both quick-start guides with the proxy's actual default port (4000). The previous 4101 URLs sent new contributors to a port where the OTLP proxy does not listen.

The new repository contract test derives the expected port from apps/proxy/.env.example, so future runtime-default changes must update the public setup instructions too.

Fixes #397

How to test

• pnpm test:repository-contracts
• pnpm test:ci-workflows
• pnpm typecheck
• pnpm exec biome check scripts/quick-start-defaults.test.ts package.json

AI assistance

• None
• Used AI for: reproducing the documentation/runtime mismatch, drafting the fix, and adding the repository contract test

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would change existing behavior)
• Documentation
• Tests only
• Refactor / cleanup

Checklist

• pnpm typecheck passes
• pnpm lint passes (current main has unrelated existing Biome diagnostics; all changed Biome-supported files pass targeted checks)
• pnpm format has been run on changed files
• Added or updated tests where it makes sense
• Branch is up to date with main
• PR title follows the area-prefix style for the area being changed
• Read CONTRIBUTING.md

---

Summary by cubic

Fixes quick-start docs that pointed OTLP traffic to port 4101 by aligning them to the proxy’s actual default port, 4000. Adds a repository contract test and CI check to keep docs in sync with apps/proxy/.env.example. Fixes #397.

• Bug Fixes
  • Updated README.md and CONTRIBUTING.md to use http://localhost:4000 for the OTLP proxy.
  • Added scripts/quick-start-defaults.test.ts and a test:repository-contracts script; CI now runs it to ensure docs match the port in apps/proxy/.env.example.

^{Written for commit 983e957. Summary will update on new commits.}

[superlog-app]

Observability review

All clear — no observability concerns found.

Bugs are afraid.

[cubic-dev-ai]

No issues found across 5 files

_{Re-trigger cubic}