feat: OpenMesh 基础平台与 MD/PDF 转换技能

- 后端: coworker 智能体框架, WS API, 文件上传, 附件处理
- 前端: Open WebUI, 文件全量走 upload API (含 MD/TXT/JSON 等文本类)
- 技能: md-to-office (pandoc + wkhtmltopdf)
- 修复: 上传文件路径丢失, Agent 搜索浪费, 输出文件跑到 uploads/
- 打包: PyInstaller one-dir, 预打包 pandoc/wkhtmltopdf/chromium

coworker/web/__init__.py

@@ -0,0 +1,29 @@
+"""Web search — a keyless DuckDuckGo default + configurable third-party providers."""
+
+from __future__ import annotations
+
+from .providers import (
+    BraveProvider,
+    DuckDuckGoProvider,
+    SearchResult,
+    TavilyProvider,
+    WebSearchProvider,
+    build_provider,
+    provider_names,
+)
+from .fetch import make_web_fetch_tool
+from .tool import make_web_search_tool, provider_name, resolve_provider
+
+__all__ = [
+    "SearchResult",
+    "WebSearchProvider",
+    "DuckDuckGoProvider",
+    "TavilyProvider",
+    "BraveProvider",
+    "build_provider",
+    "provider_names",
+    "make_web_search_tool",
+    "make_web_fetch_tool",
+    "provider_name",
+    "resolve_provider",
+]