refactor(stores): reorganize flat store files into modular directory structure

Migrate from flat file organization to modular directory structure under src/stores/:

- auth/: authStore, registerStore, verificationStore, sessionStore
- call/: callStore
- settings/: chatSettingsStore, themeStore
- ui/: homeTabBarVisibilityStore, homeTabPressStore
- utils/: routePayloadCache
- group/sources.ts, group/profileResolver.ts
- message/sources.ts
- post/sources.ts

Update all import paths across components and screens to use new module paths. Maintain backward compatibility through deprecated re-export files for gradual migration.

src/stores/utils/routePayloadCache.ts

@@ -0,0 +1,33 @@
+/**
+ * 不可放入 URL 的路由载荷（系统消息对象、课表课程对象等）的短时缓存。
+ * 深链仅带 id；从通知列表等入口跳转前先 stash，目标屏按 id 读取。
+ */
+import type { SystemMessageResponse } from '../../types/dto';
+import type { Course } from '../../types/schedule';
+
+const systemById = new Map<string, SystemMessageResponse>();
+const courseById = new Map<string, { course: Course; relatedCourses: Course[] }>();
+
+export const routePayloadCache = {
+  stashSystemMessage(message: SystemMessageResponse): void {
+    systemById.set(message.id, message);
+  },
+
+  getSystemMessage(id: string): SystemMessageResponse | undefined {
+    return systemById.get(id);
+  },
+
+  stashCourseDetail(course: Course, relatedCourses: Course[]): void {
+    courseById.set(String(course.id), { course, relatedCourses });
+  },
+
+  getCourseDetail(id: string): { course: Course; relatedCourses: Course[] } | undefined {
+    return courseById.get(id);
+  },
+
+  takeCourseDetail(id: string): { course: Course; relatedCourses: Course[] } | undefined {
+    const v = courseById.get(id);
+    if (v) courseById.delete(id);
+    return v;
+  },
+};