Concepts docs: E2EE device identity & key lifecycle (backend)

[codebestia]

Write apps/backend/docs/concepts-e2ee-key-management.md explaining the backend's role in the E2EE key lifecycle: device registration, prekey upload/consumption, key-bundle fetch, revocation, and how the devices/devicePrekeys tables model this.

Acceptance criteria:

• Explains device registration through to revocation as one coherent lifecycle, referencing the actual routes/tables involved by name
• Explains what the server can and cannot see (no private key material ever touches the backend) as an explicit statement
• Cross-references the relevant api-*.md and contracts-*.md docs

[adeboladee]

@adeboladee has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello Maintainer, Please I would like to work on this issue

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[Kingvic300]

@Kingvic300 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I would love to work on this kindly assign it to me

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[drips-wave]

Congratulations, @Kingvic300! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @Kingvic300: 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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[Ayooo-web]

@Ayooo-web has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Can i please work on this

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[flare-999]

@flare-999 has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

I'm interested on working on this
could you assign this issue to me

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[Dannyorji]

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

I will like to work on this

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

[drips-wave]

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

🧑‍💻 @Dannyorji: 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.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊