feat(theme): 专业主题系统重构 — Warp/Linear 设计参考，深色/浅色完整适配

参考设计系统:
- Warp: 温暖暗色调、自然层次、克制配色
- Linear: 亮度阶梯层次、半透明边框、精确排版

核心改进:
- app-theme.ts: 完整重写深色/浅色调色板 (+surface-hover/active, border-subtle/focus, feedback-bg, placeholder)
- useTheme.ts: 修复硬编码 return 'dark'，支持 dark/light/system 完整切换
- index.css: 消除硬编码颜色，全部使用 CSS 变量
- tailwind.config.js: 新增 txt/content/surface/border/ph/feedback 语义 token
- 44 文件批量迁移: 292 处 text-gray/bg-gray/text-white/placeholder-gray → 主题感知语义 token

| 44 files +611/-482 | tsc零错误 | 96/96 tests passing

src/components/common/CommandPalette.tsx

@@ -45,9 +45,9 @@ interface CommandPaletteProps {
 // ─── 类型 badge 颜色映射 ──────────────────────────────────────────────
 
 const TYPE_BADGE: Record<CommandPaletteItemType, { label: string; className: string }> = {
-  command: { label: '命令', className: 'bg-accent-blue/20 text-accent-blue' },
-  session: { label: '会话', className: 'bg-accent-green/20 text-accent-green' },
-  snippet: { label: '片段', className: 'bg-accent-purple/20 text-accent-purple' },
+  command: { label: '命令', className: 'bg-surface-baseccent-blue/20 text-accent-blue' },
+  session: { label: '会话', className: 'bg-surface-baseccent-green/20 text-accent-green' },
+  snippet: { label: '片段', className: 'bg-surface-baseccent-purple/20 text-accent-purple' },
 }
 
 // ─── 组件 ──────────────────────────────────────────────────────────────
@@ -305,7 +305,7 @@ export function CommandPalette({
       onKeyDown={handleKeyDown}
     >
       {/* Backdrop */}
-      <div className="absolute inset-0 bg-black/60 backdrop-blur-sm animate-fade-in" />
+      <div className="absolute inset-0 bg-surface-baselack/60 backdrop-blur-sm animate-fade-in" />
 
       {/* Palette container */}
       <div
@@ -316,18 +316,18 @@ export function CommandPalette({
       >
         {/* Search input */}
         <div className="flex items-center gap-3 px-4 py-3 border-b border-dark-700">
-          <Search size={18} className="text-gray-400 flex-shrink-0" />
+          <Search size={18} className="text-txt-muted flex-shrink-0" />
           <input
             ref={inputRef}
             type="text"
             value={query}
             onChange={(e) => setQuery(e.target.value)}
             placeholder="搜索命令、会话或片段..."
-            className="flex-1 bg-transparent text-gray-200 placeholder-gray-500 outline-none text-sm"
+            className="flex-1 bg-transparent text-content-primary placeholder-ph outline-none text-sm"
             autoComplete="off"
             spellCheck={false}
           />
-          <kbd className="hidden sm:inline-flex items-center gap-0.5 px-1.5 py-0.5 text-[10px] text-gray-500 bg-dark-700 rounded border border-dark-600">
+          <kbd className="hidden sm:inline-flex items-center gap-0.5 px-1.5 py-0.5 text-[10px] text-txt-muted bg-dark-700 rounded border border-dark-600">
             ESC
           </kbd>
         </div>
@@ -335,10 +335,10 @@ export function CommandPalette({
         {/* Results list */}
         <div ref={listRef} className="flex-1 overflow-y-auto py-1">
           {filteredItems.length === 0 ? (
-            <div className="flex flex-col items-center justify-center py-12 text-gray-500">
+            <div className="flex flex-col items-center justify-center py-12 text-txt-muted">
               <Search size={32} className="mb-2 opacity-30" />
               <p className="text-sm">没有找到匹配的结果</p>
-              <p className="text-xs text-gray-600 mt-1">试试其他关键词</p>
+              <p className="text-xs text-txt-faint mt-1">试试其他关键词</p>
             </div>
           ) : (
             groupedItems.map((group) => {
@@ -348,14 +348,14 @@ export function CommandPalette({
               return (
                 <div key={group.type}>
                   {/* Group header */}
-                  <div className="flex items-center gap-2 px-4 py-1.5 text-[11px] font-medium text-gray-500 uppercase tracking-wider">
+                  <div className="flex items-center gap-2 px-4 py-1.5 text-[11px] font-medium text-txt-muted uppercase tracking-wider">
                     <span
                       className={`inline-flex items-center px-1.5 py-0.5 rounded text-[10px] font-semibold ${TYPE_BADGE[group.type].className}`}
                     >
                       {TYPE_BADGE[group.type].label}
                     </span>
                     <span className="flex-1 h-px bg-dark-700" />
-                    <span className="text-gray-600">{group.items.length}</span>
+                    <span className="text-txt-faint">{group.items.length}</span>
                   </div>
 
                   {/* Group items */}
@@ -369,8 +369,8 @@ export function CommandPalette({
                         className={`
                           flex items-center gap-3 px-4 py-2 cursor-pointer transition-colors duration-75
                           ${isSelected
-                            ? 'bg-accent-blue/15 text-gray-100'
-                            : 'text-gray-300 hover:bg-dark-700'
+                            ? 'bg-surface-baseccent-blue/15 text-content-primary'
+                            : 'text-content-secondary hover:bg-dark-700'
                           }
                         `}
                         onClick={() => {
@@ -382,7 +382,7 @@ export function CommandPalette({
                         {/* Icon */}
                         <span
                           className={`flex-shrink-0 w-5 h-5 flex items-center justify-center ${
-                            isSelected ? 'text-accent-blue' : 'text-gray-500'
+                            isSelected ? 'text-accent-blue' : 'text-txt-muted'
                           }`}
                         >
                           {item.icon}
@@ -392,7 +392,7 @@ export function CommandPalette({
                         <div className="flex-1 min-w-0">
                           <div className="text-sm truncate">{item.label}</div>
                           {item.description && (
-                            <div className="text-[11px] text-gray-500 truncate">
+                            <div className="text-[11px] text-txt-muted truncate">
                               {item.description}
                             </div>
                           )}
@@ -400,7 +400,7 @@ export function CommandPalette({
 
                         {/* Shortcut */}
                         {item.shortcut && (
-                          <kbd className="flex-shrink-0 text-[11px] text-gray-500 bg-dark-700 px-1.5 py-0.5 rounded border border-dark-600">
+                          <kbd className="flex-shrink-0 text-[11px] text-txt-muted bg-dark-700 px-1.5 py-0.5 rounded border border-dark-600">
                             {item.shortcut}
                           </kbd>
                         )}
@@ -421,7 +421,7 @@ export function CommandPalette({
         </div>
 
         {/* Footer hint */}
-        <div className="flex items-center justify-between px-4 py-2 border-t border-dark-700 text-[11px] text-gray-600">
+        <div className="flex items-center justify-between px-4 py-2 border-t border-dark-700 text-[11px] text-txt-faint">
           <div className="flex items-center gap-3">
             <span className="flex items-center gap-1">
               <kbd className="px-1 py-0.5 bg-dark-700 rounded border border-dark-600">↑↓</kbd>