fix: data_collection_permissions.required must be array ["none"]

Per Mozilla docs, required is an array of data type strings.
For extensions that collect no data: ["none"].
Source: https://extensionworkshop.com/documentation/develop/firefox-builtin-data-consent/

https://claude.ai/code/session_01KF4i7Ra7zCEDskxDBaNtcT

manifest.json

@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "Silent Send",
-  "version": "0.9.8",
+  "version": "0.9.9",
   "description": "Intercepts personal info and substitutes it with user-defined replacements before sending to AI services.",
   "permissions": [
     "storage",