feat(cli): stamp global.agent.version from the image tag on helm deploys

With agentex-agent chart >=0.6.0 (sgp#5466) the value lands as the pod's
AGENT_VERSION, which the SGP tracing processor stamps onto every span as
__agent_version__. Old charts ignore the key, so ordering is free.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: max-parke-scale

src/agentex/lib/cli/handlers/deploy_handlers.py

@@ -279,6 +279,9 @@ def merge_deployment_configs(
                 "name": manifest.agent.name,
                 "description": manifest.agent.description,
                 "acp_type": manifest.agent.acp_type,
+                # Rendered as the pod's AGENT_VERSION (chart >=0.6.0), stamped
+                # onto every span as __agent_version__ by the SGP processor.
+                "version": image_tag,
             },
         },
         "replicaCount": manifest.deployment.global_config.replicaCount,