feat: add web search tool using SearXNG

Add WebSearchTool that queries the self-hosted SearXNG metasearch engine
for current information, documentation, and facts beyond training data.

- Add SEARXNG_URL and SEARXNG_TIMEOUT config settings
- Create WebSearchTool with query, num_results, categories params
- Register web_search tool with explore agent
- Add 10 tests for search functionality

Usage: Agents can now use web_search(query="...") to find current info.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

webber-api/src/shared/config.py

@@ -71,6 +71,10 @@ class Settings(BaseSettings):
     tatlock_api_url: str | None = "http://192.168.86.149:8000"
     internal_api_key: str | None = None
 
+    # Web search - SearXNG (use SEARXNG_URL env var to override)
+    searxng_url: str = "http://192.168.86.149:8087"
+    searxng_timeout: int = 10
+
     # Tool execution
     tool_timeout_seconds: int = 120
     sandbox_enabled: bool = True