feat: use architecture_sources API instead of per-arch deploys

Single agent creation with architecture_sources array instead of
deploying separate agents per architecture. Matches backend API redesign.

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

Author: jason-rl

action.yml

@@ -76,22 +76,22 @@ inputs:
     required: false
     # default is 'undefined' => don't auto-delete
 
-  architecture:
-    description: 'Target architecture for the agent (x86_64 or arm64). If unset, agent is universal.'
+  architectures:
+    description: 'Comma-separated target architectures (e.g., "x86_64,arm64"). Deploys once per architecture. If unset, deploys a single universal agent.'
     required: false
 
 outputs:
   agent-id:
-    description: 'The ID of the created agent (e.g., agt_xxxx)'
+    description: 'The ID of the created agent (or last deployed agent if multiple architectures)'
 
   object-id:
     description: 'The ID of the uploaded object (if applicable, e.g., obj_xxxx)'
 
   agent-name:
     description: 'The final name of the created agent'
 
-  architecture:
-    description: 'The architecture of the created agent (if specified)'
+  architectures:
+    description: 'The architectures deployed (comma-separated, if specified)'
 
 runs:
   using: 'node20'