docs: restore border-radius with consistent application

Bring back border-radius to fix diagonal border artifacts while
maintaining a cohesive look throughout the UI.

Changes:
- Set consistent border-radius values (lg: 8px, md: 6px, sm: 4px, xs: 3px)
- Apply to blockquotes (fixes diagonal corner issue)
- Apply to inline code (xs: 3px)
- Apply to code blocks (md: 6px)
- Already applied to: tables, details, mermaid, images, kbd, search

All UI elements now have matching rounded corners for a polished,
consistent appearance.

Author: ammar-agent

docs/theme/custom.css

@@ -27,10 +27,10 @@
   --link-color: rgb(62, 140, 218);
   --link-hover: var(--color-plan-mode-hover);
   --content-max-width: 78ch;
-  --radius-lg: 0;
-  --radius-md: 0;
-  --radius-sm: 0;
-  --radius-xs: 0;
+  --radius-lg: 8px;
+  --radius-md: 6px;
+  --radius-sm: 4px;
+  --radius-xs: 3px;
   --shadow-1: 0 1px 1px hsl(0 0% 0% / 0.25);
   --shadow-2: 0 2px 10px hsl(0 0% 0% / 0.35);
 
@@ -233,12 +233,14 @@ p:has(+ ol) {
   padding: 2px 6px;
   font-family: var(--font-monospace);
   font-size: 0.92em;
+  border-radius: var(--radius-xs);
 }
 
 /* Code blocks */
 pre {
   background: var(--color-background-secondary) !important;
   border: 1px solid var(--color-border) !important;
+  border-radius: var(--radius-md);
   box-shadow: var(--shadow-1);
   overflow: auto;
   margin: 1rem 0;
@@ -297,6 +299,7 @@ blockquote {
   background: color-mix(in srgb, var(--color-background-secondary), white 3%);
   padding: 1rem 1.2rem;
   margin: 1.5rem 0;
+  border-radius: var(--radius-md);
   color: var(--color-text);
 }