Fix layout width inconsistency in documentation pages

Replace CSS Grid 1fr fractional units with fixed 960px widths to ensure
consistent layout across all documentation pages. This eliminates the
57.109px width difference that caused horizontal 'jump' effect when
navigating between pages like /getting-started/introduction and
/getting-started/installation.

- Changed grid-cols-[300px_1fr_16%] to grid-cols-[300px_960px_16%]
- Changed grid-cols-[300px_1fr] to grid-cols-[300px_960px]
- Tested locally: both pages now have identical 800px article widths
- Verified elimination of horizontal layout shift between pages

Co-Authored-By: [email protected] <[email protected]>

Author: devin-ai-integration[bot]

pcweb/templates/docpage/docpage.py

@@ -617,8 +617,8 @@ def wrapper(*args, **kwargs) -> rx.Component:
 
             grid_cols_classes = "grid-cols-1"
             if show_right_sidebar:
-                grid_cols_classes += " 2xl:grid-cols-[300px_1fr_16%]"
-            grid_cols_classes += " lg:grid-cols-[300px_1fr]"
+                grid_cols_classes += " 2xl:grid-cols-[300px_960px_16%]"
+            grid_cols_classes += " lg:grid-cols-[300px_960px]"
 
             return rx.box(
                 navbar(),