feat(renderer): platform-gated dual renderer backend with isolated QtWebEngine profiles

Windows prefers WebView2, Linux uses QtWebEngine only; pythonnet deps are win32-marked. Each QtWebEngine instance gets its own profile under data/webengine, and Chromium flags are sanitized before QApplication (--no-sandbox accepted only for explicit root/container use).

requirements.txt

@@ -19,13 +19,26 @@ PyQt6-WebEngine-Qt6==6.10.2
 # ---- 大模型 SDK（OpenAI 兼容接口；DeepSeek / opencode-go / 自建反代均走它）----
 openai==2.26.0
 
-# ---- WebView2 绑定：pythonnet（import clr）+ 其加载器 ----
-pythonnet==3.1.0
-clr_loader==0.3.1
+# ---- WebView2 绑定：pythonnet（import clr）+ 其加载器（仅 Windows；Linux 自动跳过）----
+pythonnet==3.1.0; sys_platform == "win32"
+clr_loader==0.3.1; sys_platform == "win32"
 
 # ---- PDF 附件解析（ui/views/main_window.py → tools/builtin_tools/pdf_reader.py）----
 PyMuPDF==1.28.0
 
+# ===========================================================================
+# Linux 源码运行（Ubuntu 22.04/24.04 x64，仅 QtWebEngine；不装 WebView2 任何东西）
+# ===========================================================================
+# 1) pip install -r requirements.txt   # pythonnet/clr_loader 带平台 marker，Linux 自动跳过
+# 2) 安装 QtWebEngine 运行所需的系统库（apt，按需选装）：
+#       sudo apt install -y libnss3 libxkbcommon0 libfontconfig1 libdbus-1-3 \
+#            libgl1 libegl1 libasound2t64   # 24.04 用 libasound2t64；22.04 用 libasound2
+#    离屏测试另需：QT_QPA_PLATFORM=offscreen
+# 3) 运行：python3.10 main.py
+#    - 只使用 QtWebEngine；每实例独立 profile（data/webengine/profile_<pid>_*）
+#    - root/容器启动若页面空白：显式 QTWEBENGINE_CHROMIUM_FLAGS="--no-sandbox" python3.10 main.py
+#      （启动会打印高可见风险警告；普通桌面不要加）
+
 # ===========================================================================
 # 以下仅在需要时安装
 # ===========================================================================