docs: add end-to-end integration walkthrough for embedding the SDK

[karagozemin]

Summary

Expand docs/INTEGRATION.md with a complete, copy-paste walkthrough covering install → create round → commit sealed bid → open reveal → settle → export receipt.

Motivation

README.md promises reusable infrastructure, but there is no single continuous example a partner team can follow start to finish.

Acceptance criteria

• Numbered walkthrough with runnable snippets.
• Notes on required env / keys and testnet vs mainnet.
• Link-checked (scripts/check-links.js).
• Cross-linked from README.

[benzy018]

Good day, Maintainer. I'll validate the workflow from a fresh setup before submitting a clean pull request. I would appreciate being assigned this issue.

[blvckmamba81-sketch]

Hi! I'd like to work on this issue. I have experience writing clear technical documentation and can create a concise end-to-end integration walkthrough that makes embedding the SDK straightforward for developers. Thank you!

[latiblack]

Hey Karagozemin, would like to work on this, I'll expand docs/INTEGRATION.md with a numbered, copy-paste walkthrough so a partner team can embed the Sub-Rosa SDK end-to-end. I'll ground every snippet in the repo's actual surface, then export the receipt via the real pnpm --filter @sub-rosa/receipt-cli receipt export command (per docs/RECEIPTS.md). I'll add a testnet-vs-mainnet/env-keys note and verify all links with scripts/check-links.js. README already links the doc.

[grantfox-oss]

🦊 GrantFox — @latiblack has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #156)
2. Your PR will be reviewed by the Sub-Rosa-Issue maintainers

Good luck! Track your progress on GrantFox.