Prekey generation + upload + replenishment (web)

[codebestia]

Description:
Generate the signed prekey (signed by the identity key) + a batch of one-time prekeys, upload via #109, and respond to prekeys_low (#111) by generating + uploading more. Persist private prekeys in IndexedDB keyed by keyId; delete a one-time private prekey once its session is established.

Acceptance criteria:

• Signed + one-time prekeys uploaded after registration
• prekeys_low triggers replenishment
• Private prekeys stored locally, consumed once

[GreatShinro]

@GreatShinro has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, can I work on this please?

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

[Gabugo-tech]

@Gabugo-tech has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

codebestia, please kindly assign, i can work on this and submt PR within some minutes, please iw ill appreciate if you can assign this to me

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[G-ELM]

@G-ELM has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi Maintainer
I will like to work on this.
Please assign
Thanks.

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[Caneryy]

@Caneryy has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, I'd like to work on this issue please.

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[drips-wave]

Congratulations, @G-ELM! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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