fix(orchestrator): make provider-aware Claude key startup requirements

apps/orchestrator/.env.example

@@ -1,6 +1,8 @@
 # Orchestrator Configuration
 ORCHESTRATOR_PORT=3001
 NODE_ENV=development
+# AI provider for orchestrator agents: ollama, claude, openai
+AI_PROVIDER=ollama
 
 # Valkey
 VALKEY_HOST=localhost
@@ -8,6 +10,7 @@ VALKEY_PORT=6379
 VALKEY_URL=redis://localhost:6379
 
 # Claude API
+# Required only when AI_PROVIDER=claude.
 CLAUDE_API_KEY=your-api-key-here
 
 # Docker