Use ethers.js Mnemonic for real BIP-39 phrase generation

Replace stub wordlist with ethers.Mnemonic.fromEntropy() using
crypto.getRandomValues(). Add esbuild to bundle popup JS so it
can import ethers directly — no background messaging needed.
Each die click now generates a valid, random BIP-39 mnemonic.

build.js

@@ -1,6 +1,7 @@
 const fs = require("fs");
 const path = require("path");
 const { execSync } = require("child_process");
+const esbuild = require("esbuild");
 
 const DIST_CHROME = path.join(__dirname, "dist", "chrome");
 const DIST_FIREFOX = path.join(__dirname, "dist", "firefox");
@@ -10,24 +11,7 @@ function ensureDir(dir) {
     fs.mkdirSync(dir, { recursive: true });
 }
 
-function copyDir(src, dest, opts = {}) {
-    ensureDir(dest);
-    const entries = fs.readdirSync(src, { withFileTypes: true });
-    for (const entry of entries) {
-        const srcPath = path.join(src, entry.name);
-        const destPath = path.join(dest, entry.name);
-        if (opts.skip && opts.skip.includes(entry.name)) {
-            continue;
-        }
-        if (entry.isDirectory()) {
-            copyDir(srcPath, destPath, opts);
-        } else {
-            fs.copyFileSync(srcPath, destPath);
-        }
-    }
-}
-
-function build() {
+async function build() {
     console.log("Building AutistMask extension...");
 
     // compile tailwind CSS
@@ -40,21 +24,49 @@ function build() {
         { stdio: "inherit" },
     );
 
-    // copy source files (skip the styles dir, we compiled it)
     for (const distDir of [DIST_CHROME, DIST_FIREFOX]) {
-        ensureDir(distDir);
-        copyDir(path.join(SRC, "popup"), path.join(distDir, "src", "popup"), {
-            skip: ["styles"],
+        ensureDir(path.join(distDir, "src", "popup"));
+        ensureDir(path.join(distDir, "src", "background"));
+        ensureDir(path.join(distDir, "src", "content"));
+
+        // bundle popup JS with esbuild (inlines ethers, libsodium, etc.)
+        await esbuild.build({
+            entryPoints: [path.join(SRC, "popup", "index.js")],
+            bundle: true,
+            format: "iife",
+            outfile: path.join(distDir, "src", "popup", "index.js"),
+            platform: "browser",
+            target: ["chrome110", "firefox110"],
+            minify: true,
         });
-        copyDir(
-            path.join(SRC, "background"),
-            path.join(distDir, "src", "background"),
+
+        // bundle background script
+        await esbuild.build({
+            entryPoints: [path.join(SRC, "background", "index.js")],
+            bundle: true,
+            format: "iife",
+            outfile: path.join(distDir, "src", "background", "index.js"),
+            platform: "browser",
+            target: ["chrome110", "firefox110"],
+            minify: true,
+        });
+
+        // bundle content script
+        await esbuild.build({
+            entryPoints: [path.join(SRC, "content", "index.js")],
+            bundle: true,
+            format: "iife",
+            outfile: path.join(distDir, "src", "content", "index.js"),
+            platform: "browser",
+            target: ["chrome110", "firefox110"],
+            minify: true,
+        });
+
+        // copy popup HTML
+        fs.copyFileSync(
+            path.join(SRC, "popup", "index.html"),
+            path.join(distDir, "src", "popup", "index.html"),
         );
-        copyDir(
-            path.join(SRC, "content"),
-            path.join(distDir, "src", "content"),
-        );
-        copyDir(path.join(SRC, "shared"), path.join(distDir, "src", "shared"));
 
         // place compiled CSS next to popup HTML
         fs.copyFileSync(