feat(browser): auto-snapshot on navigate, screenshot prompt guidance

Browser tool enhancements:
- Navigate action now auto-includes snapshot result, saving one LLM round-trip
- Wait for networkidle + 800ms after navigation for SPA/JS-rendered pages
- Prompt guides agent to screenshot key results and ask user for login/CAPTCHA help
- Fixed playwright version pinned to 1.52.0; mirror fallback to official CDN on failure

Web console file/image support:
- SSE real-time push for images and files via on_event (file_to_send)
- Added /api/file endpoint to serve local files for web preview
- Frontend renders images in media-content container (survives delta/done overwrites)
- File attachment cards with download links; RFC 5987 encoding for non-ASCII filenames

Tool workspace fix:
- Inject workspace_dir as cwd into send and browser tools (previously only file tools)
- Screenshots now save to ~/cow/tmp/ instead of project directory

bridge/agent_initializer.py

@@ -366,7 +366,7 @@ class AgentInitializer:
 
                 if tool:
                     # Apply workspace config to file operation tools
-                    if tool_name in ['read', 'write', 'edit', 'bash', 'grep', 'find', 'ls', 'web_fetch']:
+                    if tool_name in ['read', 'write', 'edit', 'bash', 'grep', 'find', 'ls', 'web_fetch', 'send', 'browser']:
                         tool.config = file_config
                         tool.cwd = file_config.get("cwd", getattr(tool, 'cwd', None))
                         if 'memory_manager' in file_config: