chore: scaffold MV3 extension with TypeScript + esbuild toolchain

.gitignore

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+node_modules/
+build/
+web-ext-artifacts/
+*.xpi
+.DS_Store
+.claude/settings.local.json

esbuild.config.mjs

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+import esbuild from 'esbuild';
+import { fileURLToPath } from 'node:url';
+import { dirname, resolve } from 'node:path';
+
+const watch = process.argv.includes('--watch');
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+// isomorphic-git's `.` subpath export only points at the CJS build, which
+// does a top-level `require('crypto')` that esbuild can't bundle for the
+// browser. The package ships an ESM entry at ./index.js but the exports
+// map hides it. Redirect the bare specifier to the ESM file by hand.
+const isogitEsmPlugin = {
+  name: 'isogit-esm',
+  setup(build) {
+    const esmEntry = resolve(__dirname, 'node_modules/isomorphic-git/index.js');
+    build.onResolve({ filter: /^isomorphic-git$/ }, () => ({ path: esmEntry }));
+  },
+};
+
+const common = {
+  bundle: true,
+  format: 'iife',
+  target: ['firefox115'],
+  platform: 'browser',
+  mainFields: ['browser', 'module', 'main'],
+  conditions: ['browser', 'import', 'default'],
+  logLevel: 'info',
+  sourcemap: true,
+  minify: false,
+  define: {
+    'process.env.NODE_ENV': '"production"',
+    'global': 'globalThis',
+  },
+  plugins: [isogitEsmPlugin],
+};
+
+// Only the background bundle pulls in isomorphic-git and therefore needs
+// the Buffer polyfill. popup/options talk to the background via runtime
+// messages and stay tiny.
+const polyfillInject = [resolve(__dirname, 'src/common/polyfills.ts')];
+
+const entries = [
+  { entryPoints: ['src/background/index.ts'], outfile: 'build/background.js', inject: polyfillInject },
+  { entryPoints: ['src/popup/popup.ts'], outfile: 'build/popup.js' },
+  { entryPoints: ['src/options/options.ts'], outfile: 'build/options.js' },
+];
+
+if (watch) {
+  for (const e of entries) {
+    const ctx = await esbuild.context({ ...common, ...e });
+    await ctx.watch();
+  }
+  console.log('watching…');
+} else {
+  await Promise.all(entries.map(e => esbuild.build({ ...common, ...e })));
+  console.log('build ok');
+}

manifest.json

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+{
+  "manifest_version": 3,
+  "name": "Passchmop",
+  "version": "0.1.0",
+  "description": "Git-backed, client-side-encrypted password manager.",
+  "browser_specific_settings": {
+    "gecko": {
+      "id": "passchmop@schmop",
+      "strict_min_version": "115.0",
+      "data_collection_permissions": {
+        "required": ["none"]
+      }
+    }
+  }
+}

package.json

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+{
+  "name": "passchmop",
+  "version": "0.1.0",
+  "description": "Firefox password manager with a client-side-encrypted git-backed vault",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "build": "node esbuild.config.mjs",
+    "watch": "node esbuild.config.mjs --watch",
+    "typecheck": "tsc --noEmit",
+    "run": "web-ext run --source-dir=. --start-url=about:debugging",
+    "package": "web-ext build --source-dir=. --overwrite-dest"
+  },
+  "dependencies": {
+    "@isomorphic-git/lightning-fs": "^4.6.0",
+    "buffer": "^6.0.3",
+    "isomorphic-git": "^1.25.0"
+  },
+  "devDependencies": {
+    "@types/firefox-webext-browser": "^143.0.0",
+    "esbuild": "^0.25.0",
+    "typescript": "^6.0.3",
+    "web-ext": "^8.0.0"
+  }
+}

tsconfig.json

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+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "lib": ["ES2022", "DOM", "DOM.Iterable"],
+    "types": ["firefox-webext-browser"],
+    "strict": true,
+    "noImplicitAny": true,
+    "strictNullChecks": true,
+    "noUncheckedIndexedAccess": true,
+    "noImplicitOverride": true,
+    "noFallthroughCasesInSwitch": true,
+    "esModuleInterop": true,
+    "allowSyntheticDefaultImports": true,
+    "skipLibCheck": true,
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "noEmit": true,
+    "forceConsistentCasingInFileNames": true
+  },
+  "include": ["src/**/*.ts"]
+}