feat(品牌): 支持 _local 外部优先 Logo 与图标覆盖

新增 /admin/brand-assets 静态挂载，并在前端与桌面端统一采用外部优先、内置兜底的品牌资源解析；同时补充 BRANDING 文档与 README 入口说明。

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

interfaces/admin/static/chat.js

@@ -1934,7 +1934,8 @@ function prependMessageTime(node, tsIso) {
   node.insertBefore(el("div", { class: "chat-msg__time", text: txt }), node.firstChild);
 }
 
-const CHAT_BOT_LOGO_SRC = "/admin/assets/oliver.svg";
+const CHAT_BOT_LOGO_SRC = "/admin/brand-assets/logo.svg";
+const CHAT_BOT_LOGO_FALLBACK_SRC = "/admin/assets/oliver.svg";
 /** 内置默认用户头像（与助手头像同尺寸与底栏样式，SVG） */
 const DEFAULT_USER_AVATAR_SRC = "/admin/assets/default-user-avatar.svg";
 
@@ -1950,12 +1951,22 @@ async function loadMeProfile() {
 }
 
 function buildBotAvatarImg() {
-  return el("img", {
+  const img = el("img", {
     class: "chat-avatar chat-avatar--bot",
     src: CHAT_BOT_LOGO_SRC,
     alt: "",
     loading: "lazy",
   });
+  img.addEventListener(
+    "error",
+    () => {
+      if (img.dataset.logoFallbackApplied === "1") return;
+      img.dataset.logoFallbackApplied = "1";
+      img.src = CHAT_BOT_LOGO_FALLBACK_SRC;
+    },
+    { once: true },
+  );
+  return img;
 }
 
 function buildUserAvatarSlot() {
@@ -2331,13 +2342,21 @@ function mount(node) {
 }
 
 function buildChatBrandLogoNode() {
-  return el("div", { class: "chat-nav__brandWrap" }, [
-    el("img", {
-      class: "chat-nav__brandLogo",
-      src: "/admin/assets/oliver.svg",
-      alt: "oliver logo",
-    }),
-  ]);
+  const img = el("img", {
+    class: "chat-nav__brandLogo",
+    src: CHAT_BOT_LOGO_SRC,
+    alt: "site logo",
+  });
+  img.addEventListener(
+    "error",
+    () => {
+      if (img.dataset.logoFallbackApplied === "1") return;
+      img.dataset.logoFallbackApplied = "1";
+      img.src = CHAT_BOT_LOGO_FALLBACK_SRC;
+    },
+    { once: true },
+  );
+  return el("div", { class: "chat-nav__brandWrap" }, [img]);
 }
 
 function resolveAdminHashUrl(hashPath, sessionId) {

interfaces/admin/static/index.html

@@ -53,7 +53,12 @@
       <aside class="sidebar">
         <div class="brand">
           <div class="brand__logoWrap">
-            <img class="brand__logo" src="/admin/assets/oliver.svg" alt="oliver logo" />
+            <img
+              class="brand__logo"
+              src="/admin/brand-assets/logo.svg"
+              alt="site logo"
+              onerror="if(!this.dataset.fallback){this.dataset.fallback='1';this.src='/admin/assets/oliver.svg';}"
+            />
           </div>
         </div>
         <nav class="nav">

interfaces/http/fastapi_app.py

@@ -8,6 +8,7 @@ import asyncio
 import os
 import shutil
 from contextlib import asynccontextmanager
+from pathlib import Path
 from typing import Any
 import threading
 
@@ -230,6 +231,8 @@ async def _lifespan(app: FastAPI):  # type: ignore[no-untyped-def]
 
 def create_app() -> FastAPI:
     app = FastAPI(title="ops-gateway", version="0.1", lifespan=_lifespan)
+    brand_assets_dir = (Path(PROJECT_ROOT) / "_local" / "branding").resolve()
+    app.mount("/admin/brand-assets", StaticFiles(directory=str(brand_assets_dir), check_dir=False), name="admin-brand-assets")
     app.mount("/admin/assets", StaticFiles(directory=str(admin_static_dir())), name="admin-assets")
     app.include_router(build_admin_router())
     app.include_router(weixin_ilink_router)
@@ -239,7 +242,8 @@ def create_app() -> FastAPI:
         resp = await call_next(request)
         # Avoid stale JS/CSS after refactors (especially in Electron webview).
         # The admin SPA and /chat both load from /admin/assets/...
-        if str(request.url.path or "").startswith("/admin/assets/"):
+        req_path = str(request.url.path or "")
+        if req_path.startswith("/admin/assets/") or req_path.startswith("/admin/brand-assets/"):
             resp.headers["Cache-Control"] = "no-store, max-age=0"
             resp.headers["Pragma"] = "no-cache"
         return resp