Restore app-config branding and reliable profile images

[smshagor-dev]

Summary

Restore the stable pre-regression image/branding behavior without depending on a hardcoded upload hostname.

Fixes

• Keep local PWA favicon as bootstrap/final fallback instead of redirecting favicon/error assets to syncchat.smshagor.com.
• Drive the browser favicon from the runtime App Config appLogo.
• Preserve App Config logo as the primary header/logo source.
• Retry failed FTP-backed /uploads/... images through a safe backend image proxy before using a generic fallback.
• This covers personal profile photos and custom app logos when their direct public FTP URL is stale/unreachable.
• Proxy accepts only configured FTP storage URLs/paths and image extensions; it does not provide arbitrary URL fetching.
• Keep existing local default user/group/channel avatar fallbacks.
• Validate the new backend proxy controller/route in the backend build script.

Scope

Branding and image delivery only. No chat, call, auth, room-access, or database schema behavior changed.

[vercel]

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