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>

xtrm_agent/orchestrator.py

@@ -136,6 +136,15 @@ class Orchestrator:
             return f"Error: Agent '{agent_name}' not found"
 
         content = self.router.strip_mention(msg.content) if msg.content.startswith("@") else msg.content
+
+        # Prepend attachment content so the LLM can see it
+        if msg.attachments:
+            parts: list[str] = []
+            for att in msg.attachments:
+                parts.append(f"[Attached file: {att.filename}]\n{att.content}")
+            parts.append(content)
+            content = "\n\n".join(parts)
+
         logger.info(f"[{agent_name}] Processing: {content[:80]}")
         return await engine.run(content)