fix(secure-storage): enable platform-native keyring backends

Enable apple-native, windows-native, and linux-native features for the
keyring crate to use actual platform credential stores instead of mock
fallback. Without these features, keyring claims success but doesn't
persist to the system keychain/credential manager.

Tested on macOS with Files.com API key storage and retrieval working
correctly with support package uploads.

Author: joshrotenberg

Cargo.lock

@@ -54,7 +54,7 @@ directories = { workspace = true }
 shellexpand = "3.1"
 
 # Secure storage
-keyring = { version = "3.6", optional = true }
+keyring = { version = "3.6", optional = true, features = ["apple-native", "windows-native", "linux-native"] }
 
 [target.'cfg(unix)'.dependencies]
 pager = "0.16"