fix: add data_collection_permissions for AMO validation, bump 0.9.6

Mozilla now requires data_collection_permissions in the manifest.
Set collect_user_data: false (Silent Send collects no user data).

https://claude.ai/code/session_01KF4i7Ra7zCEDskxDBaNtcT

manifest.firefox.json

@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "Silent Send",
-  "version": "0.9.5",
+  "version": "0.9.6",
   "description": "Intercepts personal info and substitutes it with user-defined replacements before sending to AI services.",
   "browser_specific_settings": {
     "gecko": {
@@ -111,5 +111,8 @@
       "resources": ["src/content/content.js"],
       "matches": ["<all_urls>"]
     }
-  ]
+  ],
+  "data_collection_permissions": {
+    "collect_user_data": false
+  }
 }