replace copy-tests with post-set-playground script

Remove duplicate test files from problem directories and add a
post-set-playground.js script that copies tests from solution
directories to the playground on demand.

Author: kentcdodds

epicshop/copy-tests.js

@@ -0,0 +1,45 @@
+import fs from 'node:fs'
+import path from 'node:path'
+
+const srcDir = process.env.EPICSHOP_PLAYGROUND_SRC_DIR
+const destDir = process.env.EPICSHOP_PLAYGROUND_DEST_DIR
+
+if (!srcDir || !destDir) {
+	console.log('⚠️  Missing required environment variables')
+	process.exit(0)
+}
+
+// Find the corresponding solution directory for the source
+// If source is a problem dir, find the matching solution dir
+// If source is already a solution dir, use it directly
+const srcDirName = path.basename(srcDir)
+let solutionDir = srcDir
+
+if (srcDirName.includes('.problem.')) {
+	solutionDir = srcDir.replace('.problem.', '.solution.')
+} else if (!srcDirName.includes('.solution.')) {
+	// Not a problem or solution dir, nothing to do
+	process.exit(0)
+}
+
+if (!fs.existsSync(solutionDir)) {
+	console.log(`⚠️  No solution directory found: ${solutionDir}`)
+	process.exit(0)
+}
+
+// Copy test files from solution to playground
+const testFiles = fs
+	.readdirSync(solutionDir)
+	.filter((f) => f.endsWith('.test.ts'))
+
+for (const testFile of testFiles) {
+	const src = path.join(solutionDir, testFile)
+	const dest = path.join(destDir, testFile)
+
+	fs.copyFileSync(src, dest)
+	console.log(`✅ Copied ${testFile} from solution to playground`)
+}
+
+if (testFiles.length > 0) {
+	console.log(`\n📋 Copied ${testFiles.length} test file(s) to playground`)
+}