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/storage/chat/chat_storage.ts

@@ -43,7 +43,7 @@ export class ChatStorage implements IChatStorage {
   // ---- guest daily chat quota ----
 
   getGuestDailyChatQuota(): Promise<ResultT<GuestChatQuotaData | null>> {
-    // get-or-init：**有**返**有**，**无**则**用** DTO 默认**值**（`threshold` = max per day）**初**始**化**并**返**回**
+    // get-or-init：有返有，无则用 DTO 默认值（`threshold` = max per day）初始化并返回
     return SpAsyncUtil.getJson(
       StorageKeys.guestChatQuota,
       GuestChatQuotaSchema,
@@ -57,7 +57,7 @@ export class ChatStorage implements IChatStorage {
         today,
       );
       if (Result.isErr(initResult)) {
-        return existing; // **初**始**化**失**败** → **返**原**始** null
+        return existing; // 初始化失败 → 返原始 null
       }
       return {
         success: true,
@@ -78,7 +78,7 @@ export class ChatStorage implements IChatStorage {
   // ---- guest total quota ----
 
   getGuestTotalQuota(): Promise<ResultT<number | null>> {
-    // get-or-init：**有**返**有**，**无**则**用** DTO 默认**值**（`totalQuotaDefault`）**初**始**化**并**返**回**
+    // get-or-init：有返有，无则用 DTO 默认值（`totalQuotaDefault`）初始化并返回
     return SpAsyncUtil.getJson(
       StorageKeys.guestTotalQuotaRemaining,
       z.number(),