Add missing icons for pipeline agents on landing page

The proposal-triage-agent, plan-agent, and builder-agent were missing
from the AGENT_ICONS map, causing them to render with the default icon.

https://claude.ai/code/session_01KbB5BoHb4QJnMUFQwEyw4R

landing/index.html

@@ -1321,7 +1321,10 @@ npm install https://github.com/PR0M3TH3AN/TORCH/archive/refs/heads/main.tar.gz &
             'telemetry-agent': '📡',
             'test-coverage-agent': '☔',
             'ui-ux-agent': '🖼️',
-            'weekly-synthesis-agent': '🧠'
+            'weekly-synthesis-agent': '🧠',
+            'proposal-triage-agent': '📊',
+            'plan-agent': '🏗️',
+            'builder-agent': '👷'
         };
 
         const AGENT_CATEGORIES = {