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/python/README.md

@@ -75,6 +75,52 @@ screenshot = snap.capture(
 )
 ```
 
+### Dark Mode Capture
+
+```python
+# Capture in dark mode (prefers-color-scheme: dark)
+dark_screenshot = snap.capture(
+    "https://example.com",
+    dark_mode=True,
+    format="png",
+)
+```
+
+### Hide Elements Before Capture
+
+```python
+# Hide cookie banners, popups, ads
+clean_screenshot = snap.capture(
+    "https://example.com",
+    hide_selectors=[
+        ".cookie-banner", 
+        ".popup-overlay",
+        "#advertisement",
+        ".tracking-notice"
+    ],
+)
+
+# Hide single element
+single_hide = snap.capture(
+    "https://example.com", 
+    hide_selectors=".newsletter-popup",
+)
+```
+
+### Combined Dark Mode + Element Hiding
+
+```python
+# Perfect for clean marketing screenshots
+marketing_shot = snap.capture(
+    "https://your-saas-app.com",
+    dark_mode=True,
+    hide_selectors=[".dev-banner", ".beta-notice"],
+    width=1920,
+    height=1080,
+    device_scale=2,
+)
+```
+
 ### Error Handling
 
 ```python
@@ -106,6 +152,8 @@ except SnapAPIError as e:
 | `device_scale` | `float` | `1` | Device pixel ratio (1–3) |
 | `delay` | `int` | `0` | Extra delay in ms (0–5000) |
 | `wait_until` | `str` | `"domcontentloaded"` | Load event |
+| `dark_mode` | `bool` | `False` | Emulate prefers-color-scheme: dark |
+| `hide_selectors` | `list` | — | CSS selectors to hide before capture |
 
 ### `snap.health() -> dict`