Fix terminal color contrast and differentiation in zed-one-dark theme

- Adjust normal black from #282c33 to #5c6370 to improve visibility against background
- Implement proper bright/normal color variants with increased luminosity for bright colors
- Update preview image to reflect corrected color palette
- Resolves poor contrast for black text on dark background

Author: kavhnr

standard/previews/zed-one-dark.yaml.svg

@@ -6,20 +6,20 @@ foreground: '#dce0e5'
 details: darker
 terminal_colors:
   bright:
-    black: '#525561'
-    blue: '#74ade8'
-    cyan: '#6eb4bf'
-    green: '#a1c181'
-    magenta: '#be5046'
-    red: '#d07277'
-    white: '#dce0e5'
-    yellow: '#dec184'
+    black: '#7c8696'
+    blue: '#8bb8f0'
+    cyan: '#7ec4d0'
+    green: '#b5d196'
+    magenta: '#d16b61'
+    red: '#e6878c'
+    white: '#f0f3f8'
+    yellow: '#f0d89a'
   normal:
-    black: '#282c33'
-    blue: '#74ade8'
-    cyan: '#6eb4bf'
-    green: '#a1c181'
-    magenta: '#be5046'
-    red: '#d07277'
-    white: '#dce0e5'
-    yellow: '#dec184'
+    black: '#5c6370'
+    blue: '#61afef'
+    cyan: '#56b6c2'
+    green: '#98c379'
+    magenta: '#c678dd'
+    red: '#e06c75'
+    white: '#abb2bf'
+    yellow: '#e5c07b'