chore: move to tsdown (#1211)

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

packages/build-config/src/tsdown.base.ts

@@ -0,0 +1,46 @@
+/**
+ * Base tsdown configuration for Task Master monorepo
+ * Provides shared configuration that can be extended by individual packages
+ */
+import type { UserConfig } from 'tsdown';
+
+const isProduction = process.env.NODE_ENV === 'production';
+const isDevelopment = !isProduction;
+
+/**
+ * Environment helpers
+ */
+export const env = {
+	isProduction,
+	isDevelopment,
+	NODE_ENV: process.env.NODE_ENV || 'development'
+};
+
+/**
+ * Base tsdown configuration for all packages
+ * Since everything gets bundled into root dist/ anyway, use consistent settings
+ */
+export const baseConfig: Partial<UserConfig> = {
+	sourcemap: isDevelopment,
+	format: 'esm',
+	platform: 'node',
+	dts: isDevelopment,
+	minify: isProduction,
+	treeshake: isProduction,
+	// Keep all npm dependencies external (available via node_modules)
+	external: [/^[^@./]/, /^@(?!tm\/)/]
+};
+
+/**
+ * Utility function to merge configurations
+ * Simplified for tsdown usage
+ */
+export function mergeConfig(
+	base: Partial<UserConfig>,
+	overrides: Partial<UserConfig>
+): Partial<UserConfig> {
+	return {
+		...base,
+		...overrides
+	};
+}