feat: add extension scaffolding

Manifest, package.json, tsconfig, webpack config, popup HTML shell,
WASM type declarations, and .gitignore entries for the Chrome MV3 extension.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

extension/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "idfoto-extension",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "build": "webpack --mode production",
+    "dev": "webpack --mode development --watch",
+    "build:wasm": "wasm-pack build ../crates/idfoto-wasm --target web --out-dir ../../extension/wasm",
+    "build:all": "npm run build:wasm && npm run build"
+  },
+  "devDependencies": {
+    "@types/chrome": "^0.1.40",
+    "copy-webpack-plugin": "^12.0",
+    "ts-loader": "^9.5",
+    "typescript": "^5.4",
+    "webpack": "^5.90",
+    "webpack-cli": "^5.1"
+  }
+}