Harden X4 firmware configuration and network quotes

[noah-ing]

Summary

• present X4 as a hardware-specific prototype with explicit backup and flashing constraints
• move holdings and Wi-Fi values to an ignored local configuration and preserve configured holdings at startup
• require clock synchronization and verified TLS for quote requests, pin the build inputs, and add MIT licensing, security guidance, and read-only CI

Verification

• platformio run -e xteink_x4_release
• release build succeeded: 37.9% RAM and 17.1% flash
• static configuration checks and git diff --check

No firmware was flashed to physical hardware; device validation remains a release gate.