fix: restore working injector.js + add missing get:decrypted-config handler

Restored injector.js from v2.0.14 (commit 9a11896) which:
- Requests decrypted config from background via get:decrypted-config
  message instead of passing empty arrays when data is encrypted
- Handles the identity.profiles merge correctly for background responses
- Passes ss_settings directly (not checking _ssLocalEncrypted which
  caused settings loss)

Added missing get:decrypted-config message handler to service-worker.js
which returns decrypted mappings, identity, and settings via Storage
module.

https://claude.ai/code/session_01KF4i7Ra7zCEDskxDBaNtcT

manifest.json

@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "Silent Send",
-  "version": "0.9.18",
+  "version": "0.9.19",
   "description": "Intercepts personal info and substitutes it with user-defined replacements before sending to AI services.",
   "permissions": [
     "storage",