Add comprehensive tests and docs for darkMode & hideSelectors

- Add 5 new Python tests for darkMode and hideSelectors parameters
- Update Node.js SDK README with darkMode/hideSelectors examples
- Update Python SDK README with darkMode/hideSelectors examples
- Add API reference entries for new parameters
- All tests passing: Node.js (19 tests), Python (22 tests)

Features already implemented in v0.7.0 but needed better test coverage and documentation.

sdk/node/README.md

@@ -72,6 +72,51 @@ const screenshot = await snap.capture({
 });
 ```
 
+### Dark Mode Capture
+
+```typescript
+// Capture in dark mode (prefers-color-scheme: dark)
+const darkScreenshot = await snap.capture({
+  url: 'https://example.com',
+  darkMode: true,
+  format: 'png',
+});
+```
+
+### Hide Elements Before Capture
+
+```typescript
+// Hide cookie banners, popups, ads
+const cleanScreenshot = await snap.capture({
+  url: 'https://example.com',
+  hideSelectors: [
+    '.cookie-banner',
+    '.popup-overlay', 
+    '#advertisement',
+    '.tracking-notice'
+  ],
+});
+
+// Hide single element
+const singleHide = await snap.capture('https://example.com', {
+  hideSelectors: '.newsletter-popup',
+});
+```
+
+### Combined Dark Mode + Element Hiding
+
+```typescript
+// Perfect for clean marketing screenshots
+const marketingShot = await snap.capture({
+  url: 'https://your-saas-app.com',
+  darkMode: true,
+  hideSelectors: ['.dev-banner', '.beta-notice'],
+  width: 1920,
+  height: 1080,
+  deviceScale: 2,
+});
+```
+
 ## API Reference
 
 ### `new SnapAPI(apiKey, config?)`
@@ -98,6 +143,8 @@ Returns a `Promise<Buffer>` containing the screenshot image.
 | `deviceScale` | `number` | `1` | Device pixel ratio (1–3) |
 | `delay` | `number` | `0` | Extra delay in ms (0–5000) |
 | `waitUntil` | `string` | `'domcontentloaded'` | Load event to wait for |
+| `darkMode` | `boolean` | `false` | Emulate prefers-color-scheme: dark |
+| `hideSelectors` | `string \| string[]` | — | CSS selectors to hide before capture |
 
 ### `snap.health()`