fix: restore red hover color for buttons after VitePress update

Set --vp-c-brand CSS variables to red and add !important to brand
button hover styles to override VitePress 1.6 scoped defaults.
Remove overly broad button:hover rule.

https://claude.ai/code/session_0146mVomWtPuDpvbHcB6VQwy

Author: claude

docs/.vitepress/theme/style.css

@@ -5,14 +5,13 @@
     --vp-button-brand-text: #ffffff;
     --vp-button-brand-bg-hover: #a83232;
     --vp-button-brand-border-hover: #a83232;
+    --vp-c-brand-1: #d03c4a;
+    --vp-c-brand-2: #a83232;
+    --vp-c-brand-3: #d03c4a;
 }
 
 .VPButton.brand:hover {
-    background-color: var(--vp-button-brand-bg-hover);
-    border-color: var(--vp-button-brand-border-hover);
-    color: var(--vp-button-brand-text);
-}
-
-button:hover {
-    background-color: darkred;
+    background-color: var(--vp-button-brand-bg-hover) !important;
+    border-color: var(--vp-button-brand-border-hover) !important;
+    color: var(--vp-button-brand-text) !important;
 }