Add Discord attachment reading and web search capabilities

- Discord channel now downloads and extracts text from attachments (text files, PDFs)
- Added WebSearchTool using DuckDuckGo for researcher and coder agents
- Improved WebFetchTool with User-Agent header and HTML-to-text stripping
- Added pypdf and duckduckgo-search dependencies

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

config.yaml

@@ -27,6 +27,7 @@ tools:
     - read_file
     - list_dir
     - web_fetch
+    - web_search
     - delegate
     - write_file
     - edit_file