style: 优化文本样式和可读性

- 统一使用 VSCode 主题颜色变量
   - 添加字母间距提升可读性
   - 优化工具段落和问题选项的文本显示

src/views/messageStyles.ts

@@ -512,8 +512,9 @@ export function getMessageAreaStyles(): string {
       .tool-segment-description {
         margin: 25px 0 0 0px;
         font-size: 0.9rem;
-        color: var(--vscode-descriptionForeground);
+        color: var(--vscode-foreground);
         line-height: 1.4;
+        letter-spacing: 0.5px;
       }
       .segment-tool.low-profile .tool-segment-header {
         opacity: 0.65;
@@ -530,6 +531,7 @@ export function getMessageAreaStyles(): string {
       .segment-tool.low-profile .tool-segment-result {
         opacity: 0.7;
         font-size: 12px;
+        letter-spacing: 0.5px;
       }
       .segment-question {
         background: var(--vscode-textBlockQuote-background);
@@ -551,12 +553,13 @@ export function getMessageAreaStyles(): string {
       .segment-question .question-option {
         padding: 8px 16px;
         background: #3d3f41;
-        color: #ffffff;
+        color: var(--vscode-foreground);
         border: 1px solid #474747;
         border-radius: 6px;
         cursor: pointer;
         transition: all 0.2s;
         font-size: 13px;
+        letter-spacing: 0.5px;
       }
       .segment-question .question-option:hover {
         background: #005a9e;

src/views/planCard.ts

@@ -59,7 +59,7 @@ export function getPlanCardStyles(): string {
     .plan-summary h2 { font-size: 16px; }
     .plan-summary h3 { font-size: 14px; }
     .plan-summary h4 { font-size: 13px; }
-    .plan-summary p { margin: 8px 0; }
+    .plan-summary p { margin: 8px 0; letter-spacing: 0.5px; }
     .plan-summary ul, .plan-summary ol {
       margin: 8px 0;
       padding-left: 0;

src/views/webviewContent.ts

@@ -305,7 +305,9 @@ export function getWebviewContent(
     }
     .segment-text {
       line-height: 1.6;
-      font-size:0.9rem
+      font-size:0.9rem;
+      color: var(--vscode-foreground);
+      letter-spacing: 0.5px;
     }
     .segment-tool {
       background: var(--vscode-textBlockQuote-background);