feat: add Cloud Function entry point for observatory-agents

Add unified Cloud Function entry point exposing 7 agents at
/v1/observatory/* routes with execution_metadata, layers_executed,
CORS, and GET /health contract. Update package.json with main
entry point and deploy script. Update .gcloudignore for CF deploy.

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

Author: nicholas-ruest

.gcloudignore

@@ -1,9 +1,13 @@
-# Cloud Build ignore file
-# Overrides .gitignore for gcloud builds submit
+# Cloud Functions ignore file
+# Overrides .gitignore for gcloud functions deploy
 
-.git
-.gitignore
 node_modules/
+.git/
+dist/
+target/
+*.test.ts
+
+.gitignore
 *.log
 .env
 .env.*