Move Vite build-file copying into scripts

Keep the Node.js build helper and its tests in the build-script directory
recognised by Community review. Update the Vite import and unit CI path
filters while preserving the copy behaviour and release artefacts.

scripts/copy-build-files.ts

@@ -0,0 +1,42 @@
+import { access, copyFile, mkdir } from "node:fs/promises";
+import { join } from "node:path";
+import type { Plugin } from "vite";
+
+const BUILD_FILES = ["manifest.json", "main.js", "styles.css"] as const;
+
+function hasErrorCode(error: unknown, code: string): boolean {
+    return typeof error === "object" && error !== null && "code" in error && error.code === code;
+}
+
+export function copyBuildFiles(destinations: readonly string[], sourceDirectory = process.cwd()): Plugin {
+    return {
+        name: "copy-build-files",
+        async writeBundle() {
+            let copied = false;
+            for (const destination of destinations) {
+                let destinationCreated = false;
+                for (const file of BUILD_FILES) {
+                    const source = join(sourceDirectory, file);
+                    try {
+                        await access(source);
+                    } catch (error) {
+                        if (hasErrorCode(error, "ENOENT")) continue;
+                        throw error;
+                    }
+
+                    if (!destinationCreated) {
+                        await mkdir(destination, { recursive: true });
+                        destinationCreated = true;
+                    }
+
+                    const target = join(destination, file);
+                    await copyFile(source, target);
+                    if (!copied) console.log("copied:");
+                    copied = true;
+                    console.log(`  ${source} → ${target}`);
+                }
+            }
+            if (!copied) console.log("no items to copy");
+        },
+    };
+}