feat: build pipeline — .ts → .esm.js + .yaml + .d.ts 三件套

- add command auto-detects .ts vs .esm.js input
- .ts: Bun.build → bundle + descriptor extraction + JSON Schema → .d.ts
- .esm.js: requires .yaml alongside, .d.ts optional
- JSON Schema → TypeScript type converter
- hello-world example workflow
- 63 tests pass, biome clean

Closes #7
小橘 <xiaoju@shazhou.work>

examples/hello-world.ts

@@ -19,7 +19,7 @@ export const descriptor = {
 };
 
 const greeter: Role<Roles["greeter"]> = async (ctx) => ({
-  content: "Hello, " + ctx.start.content,
+  content: `Hello, ${ctx.start.content}`,
   meta: { greeting: "Hello!" },
 });