* ✨ Add sessionKey and sessionPlacement compatability for previous clients
* ✨ Add sessionKey and sessionPlacement compatability for previous clients on backend
* ✨ Introduce extended XHTTP and external proxy settings
* ✨ Add custom SNI for proxy
* ✨ Add previous changes into React version of app
* fix(sub): isolate per-proxy tlsSettings during external-proxy iteration
cloneMap (Clash) is shallow and `newStream := stream` (JSON) is an alias,
so tlsSettings was shared across iterations. The new applyExternalProxyTLSToStream
mutates it, leaking one proxy's serverName/fingerprint/alpn into the next
(only overwritten when the next proxy explicitly sets the same field).
Add cloneStreamForExternalProxy: shallow clones the top-level stream plus
deep clones tlsSettings and tlsSettings.settings. Regression test locks
in that proxy B does not inherit proxy A's fingerprint/alpn when B leaves
them unset.
Maksim Alekseev