`file_message` WebSocket coordination event

[codebestia]

WebSocket only signals availability/metadata, never bytes. Add a file_message event carrying { messageId, conversationId, fileId } so recipients know to fetch + decrypt. Reuse the normal delivery pipeline; file bytes flow over HTTP, not the socket.

Acceptance criteria:

• WS carries only metadata; no file bytes traverse the socket
• Recipients fetch via GET /files/:id after the event
• Delivery/receipts reuse the standard pipeline

[Theraxia]

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

i would like to work on this issue, thanks

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[0xratnendra]

@0xratnendra has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi. I have reviewed this issue and would like to work on it....ETA 3hr

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[drips-wave]

Congratulations, @0xratnendra! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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