feat(sidebar): read LibreChat URL from LIBRECHAT_URL env var

Replace hardcoded localhost:3080 chat link with configurable
LIBRECHAT_URL environment variable, passed through AuthInfo to
the sidebar component.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/infrastructure/auth_check.rs

@@ -24,13 +24,18 @@ pub async fn check_auth() -> Result<AuthInfo, ServerFnError> {
         .map_err(|e| ServerFnError::new(format!("session read failed: {e}")))?;
 
     match user_state {
-        Some(u) => Ok(AuthInfo {
-            authenticated: true,
-            sub: u.sub,
-            email: u.user.email,
-            name: u.user.name,
-            avatar_url: u.user.avatar_url,
-        }),
+        Some(u) => {
+            let librechat_url = std::env::var("LIBRECHAT_URL")
+                .unwrap_or_else(|_| "http://localhost:3080".into());
+            Ok(AuthInfo {
+                authenticated: true,
+                sub: u.sub,
+                email: u.user.email,
+                name: u.user.name,
+                avatar_url: u.user.avatar_url,
+                librechat_url,
+            })
+        }
         None => Ok(AuthInfo::default()),
     }
 }