chore: 切换到 bun publish，修复 husky 路径问题，调整 diff 折叠距离，导出 VoiceContext

- publish-npm.yml: npm publish → bun publish，移除 setup-node，使用 BUN_CONFIG_TOKEN
- package.json: prepare 脚本 husky → bunx husky，版本 2.4.4 → 2.4.5
- Messages.tsx: DIFF_COLLAPSE_DISTANCE 从 0 改为 3，避免 diff 过度折叠
- voice.tsx: 导出 VoiceContext

src/components/Messages.tsx

@@ -798,7 +798,9 @@ const MessagesImpl = ({
 
     // Collapse diffs for messages beyond the latest N messages.
     // verbose (ctrl+o) overrides and always shows full diffs.
-    const DIFF_COLLAPSE_DISTANCE = 0;
+    // 0 was too aggressive — tool results are never the last message (assistant
+    // text follows), so diffs were always collapsed.  3 keeps recent edits visible.
+    const DIFF_COLLAPSE_DISTANCE = 3;
     const shouldCollapseDiffs = renderableMessages.length - 1 - index > DIFF_COLLAPSE_DISTANCE;
 
     const k = messageKey(msg);