feat: multimodal image clients, workspaces, Tushare skill, test fixes

- Replace monolithic image_message_client with HTTP/OCR/legacy modules; tighten OpenAI transport + tool schemas for multimodal downgrade to OCR specialist path.
- Add image/stock workspace prompts (META/SOUL/ROLE_SYSTEM); register experts; tweak specialist agent/direct loop/query_image_attachment.
- Add bundled runtime/skills/tushare-finance (references, api_client, SKILL metadata).
- Document OCR-related env vars; admin chat tweaks; README; weixin_install Ensure-OfficialPluginRuntimeDeps helper.
- Tests: multimodal downgrade + OCR coverage, strict tool pairing in attachment replay guard, workspace contract skips _internal/_system dirs, router/trace/prompt guards.

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

interfaces/admin/static/chat.html

@@ -574,7 +574,7 @@
     <script defer src="/admin/assets/admin-theme.js"></script>
     <script
       defer
-      src="/admin/assets/chat.js?v=20260507-2"
+      src="/admin/assets/chat.js?v=20260510-2"
       onerror="(function(){var s=document.getElementById('chat-boot-splash');if(s){s.querySelector('.chat-boot-splash__title span:last-child').textContent='无法加载 chat.js';s.querySelector('.chat-boot-splash__muted').textContent='请确认网关已启动且 /admin/assets/chat.js 可访问。';}})()"
     ></script>
   </head>