Fix base64 encoding for browser environment

The bufferToBase64 function from @binect/js expects Node.js Buffer
objects but was receiving browser ArrayBuffer, causing "[object ArrayBuffer]"
to be sent instead of valid base64. Use browser-native btoa() instead.

Also updates tests to work with @binect/js integration.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package-lock.json

@@ -8,6 +8,9 @@
       "name": "binect-chrome",
       "version": "1.0.0",
       "license": "MIT",
+      "dependencies": {
+        "@binect/js": "file:../binect-js"
+      },
       "devDependencies": {
         "@types/chrome": "^0.0.260",
         "@types/jest": "^29.5.11",
@@ -28,6 +31,19 @@
         "webpack-cli": "^5.1.4"
       }
     },
+    "../binect-js": {
+      "name": "@binect/js",
+      "version": "0.1.0",
+      "license": "MIT",
+      "devDependencies": {
+        "@types/node": "^20.10.0",
+        "typescript": "^5.3.0",
+        "vitest": "^1.0.0"
+      },
+      "engines": {
+        "node": ">=18.0.0"
+      }
+    },
     "node_modules/@babel/code-frame": {
       "version": "7.28.6",
       "resolved": "https://registry.npmjs.org/@babel/code-frame/-/code-frame-7.28.6.tgz",
@@ -545,6 +561,10 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@binect/js": {
+      "resolved": "../binect-js",
+      "link": true
+    },
     "node_modules/@discoveryjs/json-ext": {
       "version": "0.5.7",
       "resolved": "https://registry.npmjs.org/@discoveryjs/json-ext/-/json-ext-0.5.7.tgz",