fix(h5): show TKMind as the user-facing product name

Keep the chat chrome, page title, and related copy aligned with the existing TKMind brand.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/utils/appBrand.ts

@@ -1,5 +1,5 @@
 /** User-facing product name shown in nav, login, and page chrome. */
-export const APP_DISPLAY_NAME = 'Memind';
+export const APP_DISPLAY_NAME = 'TKMind';
 
 /** Branded tagline suffix used on welcome and marketing surfaces. */
 export const APP_DISPLAY_TAGLINE = `${APP_DISPLAY_NAME} 智趣`;