fix: move test suite JS to external file for Firefox CSP, bump 0.9.3

Firefox extension CSP blocks inline <script> tags. Moved all test
code to test-suite.js (loaded via src attribute). Build script updated
to copy both files.

https://claude.ai/code/session_01KF4i7Ra7zCEDskxDBaNtcT

package.json

@@ -1,6 +1,6 @@
 {
   "name": "silent-send",
-  "version": "0.9.2",
+  "version": "0.9.3",
   "private": true,
   "license": "BSL-1.1",
   "description": "Browser extension that substitutes personal data before sending to AI services",