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

src/background/service-worker.js

@@ -163,6 +163,17 @@ api.runtime.onMessage.addListener((message, sender, sendResponse) => {
 });
 
 const messageHandlers = {
+  async 'get:decrypted-config'(_message, _sender, sendResponse) {
+    try {
+      const mappings = await Storage.getMappings();
+      const identity = await Storage.getIdentity();
+      const settings = await Storage.getSettings();
+      sendResponse({ mappings, identity, settings });
+    } catch {
+      sendResponse(null);
+    }
+  },
+
   async 'substitution:performed'(message, sender) {
     const tabId = sender.tab?.id;
     if (tabId == null) return;