Give Atlas access to web_search tool

- Add web_search to ATLAS_TOOLS filter (was only finalize_prd)
- Add Tools Available section to atlas prompt so it knows when/how to use it

Made-with: Cursor

src/atlas.ts

@@ -65,7 +65,7 @@ export interface AtlasChatResult {
 // Main chat handler
 // ---------------------------------------------------------------------------
 
-const ATLAS_TOOLS = ALL_TOOLS.filter(t => t.name === 'finalize_prd');
+const ATLAS_TOOLS = ALL_TOOLS.filter(t => ['finalize_prd', 'web_search'].includes(t.name));
 
 export async function atlasChat(
     sessionId: string,