refactor(ui): unify layout system with 60rem max-width and consistent spacing

- Standardize container max-width across all panels:
  * Replace max-w-4xl and max-w-5xl with unified max-w-[60rem]
  * Apply to SettingsPage, UnifiedMcpPanel, SkillsPage, and FullScreenPanel
  * Ensures consistent reading width and visual balance on wide screens

- Optimize padding hierarchy and structure:
  * Move px-6 from parent elements to content containers
  * FullScreenPanel: Add max-w-[60rem] wrapper to header, content, and footer
  * Add border separators (border-t/border-b) to header and footer sections
  * Consolidate nested padding in MCP, Skills, and Prompts panels
  * Remove redundant padding layers for cleaner CSS

- Simplify component styling:
  * MCP list items: Replace card-based layout with modern group-based design
  * Remove unnecessary wrapper divs and flatten DOM structure
  * Update card hover effects with smooth transitions
  * Simplify icon selection dialog (remove description text in BasicFormFields)

- Benefits:
  * Consistent 60rem max-width provides optimal readability
  * Unified spacing rules reduce maintenance complexity
  * Cleaner component hierarchy improves performance
  * Better responsive behavior across different screen sizes
  * More cohesive visual design language throughout the app

This creates a maintainable, scalable design system foundation.

src/components/skills/RepoManagerPanel.tsx

@@ -93,7 +93,7 @@ export function RepoManagerPanel({
       onClose={onClose}
     >
       {/* 添加仓库表单 */}
-      <div className="space-y-4 glass-card rounded-xl p-6 border border-border/10">
+      <div className="space-y-4 glass rounded-xl p-6 border border-white/10">
         <h3 className="text-base font-semibold text-foreground">
           添加技能仓库
         </h3>
@@ -156,7 +156,7 @@ export function RepoManagerPanel({
           {t("skills.repo.list")}
         </h3>
         {repos.length === 0 ? (
-          <div className="text-center py-12 glass-card rounded-xl border border-border/10">
+          <div className="text-center py-12 glass rounded-xl border border-white/10">
             <p className="text-sm text-muted-foreground">
               {t("skills.repo.empty")}
             </p>
@@ -166,7 +166,7 @@ export function RepoManagerPanel({
             {repos.map((repo) => (
               <div
                 key={`${repo.owner}/${repo.name}`}
-                className="flex items-center justify-between rounded-xl border border-border/10 glass-card px-4 py-3"
+                className="flex items-center justify-between rounded-xl border border-white/10 bg-gray-900/40 px-4 py-3"
               >
                 <div>
                   <div className="text-sm font-medium text-foreground">