feat: add PDF render timing to convert and demo routes

- renderPdf() and renderUrlPdf() now return { pdf, durationMs }
- Timing wraps the actual render with Date.now()
- Log render duration via logger.info
- Add X-Render-Time response header in convert and demo routes
- Update all callers in convert, demo, templates routes
- Add TDD tests in render-timing.test.ts
- Update existing test mocks for new return shape

src/services/browser.ts

@@ -239,10 +239,11 @@ export interface PdfRenderOptions {
 export async function renderPdf(
   html: string,
   options: PdfRenderOptions = {}
-): Promise<Buffer> {
+): Promise<{ pdf: Buffer; durationMs: number }> {
   const { page, instance } = await acquirePage();
   try {
     await page.setJavaScriptEnabled(false);
+    const startTime = Date.now();
     const result = await Promise.race([
       (async () => {
         await page.setContent(html, { waitUntil: "domcontentloaded", timeout: 15_000 });
@@ -267,7 +268,9 @@ export async function renderPdf(
         setTimeout(() => reject(new Error("PDF_TIMEOUT")), 30_000)
       ),
     ]);
-    return result;
+    const durationMs = Date.now() - startTime;
+    logger.info(`PDF rendered in ${durationMs}ms (html, ${result.length} bytes)`);
+    return { pdf: result, durationMs };
   } finally {
     releasePage(page, instance);
   }
@@ -279,7 +282,7 @@ export async function renderUrlPdf(
     waitUntil?: string;
     hostResolverRules?: string;
   } = {}
-): Promise<Buffer> {
+): Promise<{ pdf: Buffer; durationMs: number }> {
   const { page, instance } = await acquirePage();
   try {
     await page.setJavaScriptEnabled(false);
@@ -316,6 +319,7 @@ export async function renderUrlPdf(
         });
       }
     }
+    const startTime = Date.now();
     const result = await Promise.race([
       (async () => {
         await page.goto(url, {
@@ -342,7 +346,9 @@ export async function renderUrlPdf(
         setTimeout(() => reject(new Error("PDF_TIMEOUT")), 30_000)
       ),
     ]);
-    return result;
+    const durationMs = Date.now() - startTime;
+    logger.info(`PDF rendered in ${durationMs}ms (url, ${result.length} bytes)`);
+    return { pdf: result, durationMs };
   } finally {
     releasePage(page, instance);
   }