feat: TypeScript installation wizard with @clack/prompts TUI (#1)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

src/template/engine.ts

@@ -0,0 +1,26 @@
+export interface TemplateVars {
+  [key: string]: string;
+}
+
+/**
+ * Replaces {{PLACEHOLDER}} tokens with provided values.
+ * Does NOT expand ${ENV_VAR} syntax — those pass through for shell resolution.
+ */
+export function renderTemplate(
+  template: string,
+  vars: TemplateVars,
+  options: { strict?: boolean } = {},
+): string {
+  return template.replace(
+    /\{\{([A-Z_][A-Z0-9_]*)\}\}/g,
+    (match, varName: string) => {
+      if (varName in vars) {
+        return vars[varName];
+      }
+      if (options.strict) {
+        throw new Error(`Template variable not provided: {{${varName}}}`);
+      }
+      return '';
+    },
+  );
+}