fix: move data_collection_permissions under browser_specific_settings.gecko

AMO requires the property at browser_specific_settings/gecko/data_collection_permissions,
not at the manifest root. Bump 0.9.7.

https://claude.ai/code/session_01KF4i7Ra7zCEDskxDBaNtcT

manifest.json

@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "Silent Send",
-  "version": "0.9.6",
+  "version": "0.9.7",
   "description": "Intercepts personal info and substitutes it with user-defined replacements before sending to AI services.",
   "permissions": [
     "storage",