Fix admin panel loading loop; add DOB capture and profile age visibility

[ehsanking]

Motivation

• The System Management (admin) panel could remain stuck on a loading spinner when one of the backend admin endpoints was slow or hung, blocking the whole view.
• The product requires collecting a user birth date at signup and letting users opt-in to show/hide their age publicly while preserving privacy of raw DOB.

Description

• Prevent admin loading stall by wrapping each admin data request in ChatDashboardClient with a bounded withTimeout helper so a single slow request returns null instead of blocking the entire Promise.all aggregation.
• Add day/month/year birth-date inputs to the v2 registration UI (components/auth/RegisterPageClient.tsx), validate client-side, and send birthDay/birthMonth/birthYear in the v2 registration payload via lib/e2ee-register-runtime.ts and app/api/e2ee/register/route.ts.
• Validate and persist birth date server-side in registerUser (strict calendar validation and allowed range), add birthDate and showAge fields to Prisma schemas (prisma/schema.prisma and prisma/schema.sqlite.prisma) and include a migration SQL (prisma/migrations/20260414_add_user_birthdate_and_age_visibility/migration.sql).
• Add showAge preference to profile saving flow and UI (app/chat/profile/page.tsx and app/actions/profile.actions.ts) and expose a computed age only on public profile responses when showAge is enabled (raw birthDate is not exposed in public profile output).

Testing

• Ran npm run lint with no errors (passed).
• Ran npm run build and a full Next.js production build completed successfully (static pages generated and build finished).
• Note: migration SQL was added and Prisma client was regenerated as part of the build; run prisma migrate or prisma db push in your environment to apply DB changes before running the app.

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Codex Task