refactor(splash): convert Skip to explicit guest login flow

- Splash Skip button now dispatches `AuthGuestLoginSubmitted` instead of
  direct routing, keeping guest auth under the state machine
- Update PWA install dialog copy ("Add to Home Screen") and drop favicon
  entry from manifest icons
- Add debug logging and routing sequence docs to splash-button

src/router/proxy.ts

@@ -23,11 +23,16 @@
  *   - 函数导出名建议为 `proxy`（可默认导出）。
  *
  * 用 `src/` 时 proxy 必须放在 `src/` 内（参见 `src-folder.md`）。
+ *
+ * DEBUG：每条请求都打日志（`hasSession` / `isAuthOnly` / `isProtected` + 决策），
+ *   用于排查"进入 /splash 后仍自动跳 /chat"类路由 bug。bug 修完可考虑保留 INFO 级别 + 删 DEBUG。
  */
 
 import { NextResponse } from "next/server";
 import type { NextRequest } from "next/server";
 
+import { Logger } from "@/utils/logger";
+
 import {
   AUTH_ONLY_ROUTES,
   PROTECTED_ROUTES,
@@ -40,6 +45,9 @@ const SESSION_COOKIE_NAMES = [
   "__Secure-next-auth.session-token",
 ];
 
+/** proxy 入口日志（Node.js runtime 跑，pino 兼容） */
+const log = new Logger("Proxy");
+
 function isAuthOnlyRoute(pathname: string): boolean {
   return (AUTH_ONLY_ROUTES as readonly string[]).includes(pathname);
 }
@@ -58,21 +66,38 @@ export function proxy(request: NextRequest) {
   const hasSession = SESSION_COOKIE_NAMES.some(
     (name) => Boolean(request.cookies.get(name)?.value),
   );
+  const isAuthOnly = isAuthOnlyRoute(pathname);
+  const isProtected = isProtectedRoute(pathname);
+
+  // DEBUG：每条请求都打（区分 path 1=proxy 跳 vs path 2=splash useEffect 跳）
+  log.info(
+    { pathname, hasSession, isAuthOnly, isProtected },
+    "[proxy] request",
+  );
 
   // 已登录访问未登录专属页 → /chat
-  if (hasSession && isAuthOnlyRoute(pathname)) {
+  if (hasSession && isAuthOnly) {
+    log.info(
+      { pathname, target: ROUTES.chat, reason: "logged-in → auth-only" },
+      "[proxy] redirect",
+    );
     const url = request.nextUrl.clone();
     url.pathname = ROUTES.chat;
     return NextResponse.redirect(url, 308);
   }
 
   // 未登录访问登录态专属页 → /splash（首界面）
-  if (!hasSession && isProtectedRoute(pathname)) {
+  if (!hasSession && isProtected) {
+    log.info(
+      { pathname, target: ROUTES.splash, reason: "not-logged-in → protected" },
+      "[proxy] redirect",
+    );
     const url = request.nextUrl.clone();
     url.pathname = ROUTES.splash;
     return NextResponse.redirect(url, 308);
   }
 
+  log.info({ pathname }, "[proxy] pass-through");
   return NextResponse.next();
 }