fix(error): add documentation URLs to config validation error messages

Include ERROR_DOC_CONFIG_URL in InvalidClientKey and InvalidDefaultKeysetId
error variants to help users resolve configuration issues.

Author: tobyhede

packages/cipherstash-proxy/src/error.rs

@@ -122,10 +122,10 @@ pub enum ConfigError {
     #[error(transparent)]
     FileOrEnvironment(#[from] config::ConfigError),
 
-    #[error("Client key is not valid.")]
+    #[error("Client key is not valid. For help visit {}", ERROR_DOC_CONFIG_URL)]
     InvalidClientKey,
 
-    #[error("default_keyset_id is not a valid UUID.")]
+    #[error("default_keyset_id is not a valid UUID. For help visit {}", ERROR_DOC_CONFIG_URL)]
     InvalidDefaultKeysetId,
 
     #[error("Server host {name} is not a valid server name")]