Local object store (development) reference

[codebestia]

Write apps/backend/docs/concepts-local-object-store.md for lib/localObjectStore.ts and the localStorage route: the filesystem-backed implementation of ObjectStoreLike used in development and test so presigned upload/download URLs actually work without MinIO.

Acceptance criteria:

• Documents the ObjectStoreLike surface both implementations satisfy, including headObject used by upload-confirm verification
• Explains where bytes land on disk, the signed local URL format, and how the serving route validates expiry and signature
• Documents the production/development selection and confirms no call-site changes between them
• States that this keeps the test suite free of Docker, consistent with the project's no-external-services rule

[Marywase]

@Marywase has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hello maintainer, if assigned, I’ll trace localObjectStore.ts and the localStorage serving route, document the shared ObjectStoreLike surface including headObject, explain the on-disk layout and signed URL validation, and clearly cover how development and production implementations are selected without changing call sites. I’ll also make sure the no-Docker test requirement and local upload and download flow are accurately reflected.
Thank you!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Marywase to this issue.

[Damola09]

@Damola09 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Can i work on this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Damola09 to this issue.

[drips-wave]

Congratulations, @Damola09! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on September 30, 2026.

🧑‍💻 @Damola09: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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[github-actions]

Closed by #611, merged into dev.

[drips-wave]

This issue has been completed by @Damola09 as part of the Stellar Wave Program's 9th Wave 🥳

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