feat: compress connection keys (rtun2) for easier copy/paste

droid-wiki/reference/data-models.md

@@ -4,7 +4,7 @@
 
 ```rust
 pub struct ConnectionKey {
-    pub version: u8,          // must be 1
+    pub version: u8,          // must be 2
     pub target: String,       // listener address
     pub ca_cert_pem: String,
     pub server_cert_pem: String,
@@ -15,7 +15,7 @@ pub struct ConnectionKey {
 }
 ```
 
-Encoded as: `rtun1.` + base64url(JSON) — no padding.
+Encoded as: `rtun2.` + base64url(deflate(JSON)) — no padding.
 
 ## Config