feat(docs): display compatible logo for dark mode (apache#18197)

## Which issue does this PR close?

- Closes apache#18190.

## What changes are included in this PR?

This PR adds a new asset (original_dark.svg) which is similar to
original.svg with just a change in text color from black to white, to
support proper logo display in dark mode. It also updates the relevant
files to ensure the correct logo variant is shown depending on the theme
(light or dark).

<img width="3200" height="1632" alt="Screenshot 2025-10-21 at 16-49-35
Apache DataFusion — Apache DataFusion documentation"
src="https://github.com/user-attachments/assets/b44a6e38-f7c6-4787-b35a-2361ed1ec9a8"
/>
&nbsp
<img width="3200" height="1632" alt="Screenshot 2025-10-21 at 16-49-43
Apache DataFusion — Apache DataFusion documentation"
src="https://github.com/user-attachments/assets/98953a0a-b2eb-4dc7-8acc-018f78a1730d"
/>

Author: foskey51

docs/source/_static/images/original_dark.svg

@@ -40,6 +40,18 @@ code {
   text-align: center;
 }
 
+/* Display appropriate logo for dark and light mode */
+.light-logo { display: inline; }
+.dark-logo { display: none; }
+
+@media (prefers-color-scheme: dark) {
+  .light-logo { display: none; }
+  .dark-logo { 
+    display: inline; 
+    background-color: transparent !important;
+  }
+}
+
 /* Ensure the logo is properly displayed */
 
 .navbar-brand {

docs/source/_static/theme_overrides.css

@@ -1,6 +1,7 @@
 <p>
   <a href="{{ pathto(master_doc) }}">
-    <img src="{{ pathto('_static/images/2x_bgwhite_original.png', 1) }}" class="logo" alt="logo">
+    <img src="{{ pathto('_static/images/original.svg', 1) }}" class="logo light-logo" alt="logo">
+    <img src="{{ pathto('_static/images/original_dark.svg', 1) }}" class="logo dark-logo" alt="logo">
   </a>
 </p>
 <p>

docs/source/_templates/docs-sidebar.html

@@ -15,8 +15,13 @@
 .. specific language governing permissions and limitations
 .. under the License.
 
-.. image:: _static/images/2x_bgwhite_original.png
-  :alt: DataFusion Logo
+.. image:: _static/images/original.svg
+   :alt: DataFusion Logo
+   :class: light-logo
+
+.. image:: _static/images/original_dark.svg
+   :alt: DataFusion Logo
+   :class: dark-logo
 
 =================
 Apache DataFusion