style: remove markdown bold syntax from code comments

Remove `**...**` emphasis markers from inline comments and JSDoc blocks across
auth and chat components, machine mappers, and quota helpers. These are
plain code comments, not rendered markdown, so the bold syntax was noise.

Files touched:
- src/app/auth/components/auth-screen.tsx
- src/app/chat/components/chat-header.tsx
- src/app/chat/components/chat-screen.tsx
- chat machine mapper / quota helpers

No functional or behavioral changes.

src/data/schemas/chat/chat_send_response.ts

@@ -15,7 +15,7 @@ export const ChatSendResponseSchema = z.object({
   currentMood: z.string().default(""),
   messageId: z.string(),
   isGuest: z.boolean().default(false),
-  // 函数式 default —— 每次 parse 时**重新**调 Date.now()（后端不返回 timestamp 时用**当下**时间）
+  // 函数式 default —— 每次 parse 时重新调 Date.now()（后端不返回 timestamp 时用当下时间）
   timestamp: z.number().default(() => Date.now()),
 });