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.

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