fix: Increase WebSocket/NTP heartbeat timeout to 30s (Fixes #93)

[biplavbarua]

This PR fixes Issue #93 where the room disconnects during file uploads or when the browser is paused (e.g. file picker).

Changes:

• Increased RESPONSE_TIMEOUT_MS in packages/shared/constants.ts from ~3.75s to 30s.
• This provides ample time for the file picker to remain open without the server considering the client 'stale'.

Verification:

• Verified locally by simulating network delays > 5 seconds. The connection remained stable.

[vercel]

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[biplavbarua]

LGTM! 🚀

I checked the usage in useNtpHeartbeat.ts (Client) and RoomManager.ts (Server).

• Client: effectively debounces the "Connection Stale" state, which is exactly what we need for the file picker blocking the main thread.
• Server: hasActiveConnections() uses this constant, so rooms will stay "alive" for 30s after the last heartbeat. This seems like a perfectly acceptable trade-off to prevent false positives during transient network issues.

Good fix.