feat: add darkMode and hideSelectors screenshot parameters

- darkMode: emulates prefers-color-scheme: dark before navigation
- hideSelectors: injects CSS to hide elements before capture
  - POST: accepts string or string array
  - GET: accepts comma-separated string
  - Validation: max 10 selectors, each max 200 chars
- OpenAPI docs updated for both GET and POST endpoints
- 13 new tests added (service + route)

src/services/__tests__/screenshot.test.ts

@@ -24,6 +24,8 @@ function createMockPage() {
     goto: vi.fn().mockResolvedValue(undefined),
     waitForSelector: vi.fn().mockResolvedValue(undefined),
     screenshot: vi.fn().mockResolvedValue(Buffer.from('fake-screenshot')),
+    emulateMediaFeatures: vi.fn().mockResolvedValue(undefined),
+    addStyleTag: vi.fn().mockResolvedValue(undefined),
   }
 }
 
@@ -177,6 +179,67 @@ describe('Screenshot Service', () => {
     })
   })
 
+  describe('darkMode', () => {
+    it('emulates prefers-color-scheme: dark when darkMode is true', async () => {
+      await takeScreenshot({ url: 'https://example.com', darkMode: true })
+      expect(mockPage.emulateMediaFeatures).toHaveBeenCalledWith([
+        { name: 'prefers-color-scheme', value: 'dark' }
+      ])
+    })
+
+    it('calls emulateMediaFeatures before goto', async () => {
+      const callOrder: string[] = []
+      mockPage.emulateMediaFeatures.mockImplementation(async () => { callOrder.push('emulate') })
+      mockPage.goto.mockImplementation(async () => { callOrder.push('goto') })
+      await takeScreenshot({ url: 'https://example.com', darkMode: true })
+      expect(callOrder).toEqual(['emulate', 'goto'])
+    })
+
+    it('does not emulate media features when darkMode is false', async () => {
+      await takeScreenshot({ url: 'https://example.com', darkMode: false })
+      expect(mockPage.emulateMediaFeatures).not.toHaveBeenCalled()
+    })
+
+    it('does not emulate media features when darkMode is not set', async () => {
+      await takeScreenshot({ url: 'https://example.com' })
+      expect(mockPage.emulateMediaFeatures).not.toHaveBeenCalled()
+    })
+  })
+
+  describe('hideSelectors', () => {
+    it('injects style tag to hide selectors after page load', async () => {
+      await takeScreenshot({ url: 'https://example.com', hideSelectors: ['.ad', '#banner'] })
+      expect(mockPage.addStyleTag).toHaveBeenCalledWith({
+        content: '.ad { display: none !important }\n#banner { display: none !important }'
+      })
+    })
+
+    it('calls addStyleTag after goto', async () => {
+      const callOrder: string[] = []
+      mockPage.goto.mockImplementation(async () => { callOrder.push('goto') })
+      mockPage.addStyleTag.mockImplementation(async () => { callOrder.push('addStyleTag') })
+      await takeScreenshot({ url: 'https://example.com', hideSelectors: ['.ad'] })
+      expect(callOrder.indexOf('goto')).toBeLessThan(callOrder.indexOf('addStyleTag'))
+    })
+
+    it('does not inject style tag when hideSelectors is empty', async () => {
+      await takeScreenshot({ url: 'https://example.com', hideSelectors: [] })
+      expect(mockPage.addStyleTag).not.toHaveBeenCalled()
+    })
+
+    it('does not inject style tag when hideSelectors is not set', async () => {
+      await takeScreenshot({ url: 'https://example.com' })
+      expect(mockPage.addStyleTag).not.toHaveBeenCalled()
+    })
+
+    it('handles single selector', async () => {
+      await takeScreenshot({ url: 'https://example.com', hideSelectors: ['.cookie-banner'] })
+      expect(mockPage.addStyleTag).toHaveBeenCalledWith({
+        content: '.cookie-banner { display: none !important }'
+      })
+    })
+  })
+
   describe('Page lifecycle', () => {
     it('always releases page after successful screenshot', async () => {
       await takeScreenshot({ url: 'https://example.com' })

src/services/screenshot.ts

@@ -14,6 +14,8 @@ export interface ScreenshotOptions {
   deviceScale?: number;
   delay?: number;
   waitUntil?: "load" | "domcontentloaded" | "networkidle0" | "networkidle2";
+  darkMode?: boolean;
+  hideSelectors?: string[];
 }
 
 export interface ScreenshotResult {
@@ -42,6 +44,10 @@ export async function takeScreenshot(opts: ScreenshotOptions): Promise<Screensho
   try {
     await page.setViewport({ width, height, deviceScaleFactor: deviceScale });
 
+    if (opts.darkMode) {
+      await page.emulateMediaFeatures([{ name: 'prefers-color-scheme', value: 'dark' }]);
+    }
+
     await Promise.race([
       (async () => {
         await page.goto(opts.url, { waitUntil, timeout: 20_000 });
@@ -53,6 +59,12 @@ export async function takeScreenshot(opts: ScreenshotOptions): Promise<Screensho
         if (opts.delay && opts.delay > 0) {
           await new Promise(r => setTimeout(r, Math.min(opts.delay!, 5000)));
         }
+
+        if (opts.hideSelectors && opts.hideSelectors.length > 0) {
+          await page.addStyleTag({
+            content: opts.hideSelectors.map(s => s + ' { display: none !important }').join('\n')
+          });
+        }
       })(),
       new Promise<never>((_, reject) => setTimeout(() => reject(new Error("SCREENSHOT_TIMEOUT")), TIMEOUT_MS)),
     ]);