docs(onboarding): add client starter templates

[typelicious]

What changed

• add starter example files for OpenClaw, n8n, and CLI clients under docs/examples/
• link the example files from onboarding and integration docs
• expose the examples in the main docs index

Why

• move from report-only onboarding guidance to copy/pasteable starter templates
• make many-client onboarding faster for first-time operators

How verified

• PYTHONPYCACHEPREFIX="/Users/andrelange/.codex/worktrees/257a/ClawGate/.pycache" python3 -m compileall foundrygate tests
• ./.venv-check-313/bin/ruff check README.md docs/INTEGRATIONS.md docs/ONBOARDING.md CHANGELOG.md
• bash -n docs/examples/cli-foundrygate-env.sh
• git diff --check