fix: connection stability improvements for production issues

[sanity]

Summary

• Fix graceful handling of RSA intro packets on established connections
• Make keep-alive constants consistent between debug and release builds

Fixes

1. Intro packet handling: When established connections receive 256-byte RSA intro packets (e.g., when a peer tries to reestablish), we now decrypt and ACK them instead of logging decryption errors
2. Keep-alive compatibility: Debug and release builds now use the same timing (10s interval, 30s timeout) to prevent premature connection drops

Root Cause

Production decryption errors after ~60 seconds were caused by:

• Debug/release keep-alive incompatibility causing legitimate timeouts
• Lack of graceful handling when peers sent intro packets to reestablish

Test plan

• [x] Integration tests pass
• [ ] Deploy to gateways and verify connection stability
• [ ] Monitor for decryption errors in production

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