Add project scaffolding

Makefile, Dockerfile, CI workflow, prettier config, manifests for
Chrome (MV3) and Firefox (MV2), source directory structure, and
minimal test suite. All checks pass.

manifest/chrome.json

@@ -0,0 +1,20 @@
+{
+    "manifest_version": 3,
+    "name": "AutistMask",
+    "version": "0.1.0",
+    "description": "Minimal Ethereum wallet for Chrome",
+    "permissions": ["storage", "activeTab"],
+    "action": {
+        "default_popup": "src/popup/index.html"
+    },
+    "background": {
+        "service_worker": "src/background/index.js"
+    },
+    "content_scripts": [
+        {
+            "matches": ["<all_urls>"],
+            "js": ["src/content/index.js"],
+            "run_at": "document_start"
+        }
+    ]
+}