feat: add multi-repo cloning, remove dynamic/serverless mode

Add githubRepos list field for cloning multiple repositories into a
single dev container with multi-root workspace file generation.
Remove the unused dynamic deployment mode (Knative, routing proxy,
serverless scripts) to simplify the chart to persistent-only.
Fix release workflow cache-to setting that violated the no-cache policy.

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

chart/templates/service.yaml

@@ -1,4 +1,3 @@
-{{- if eq .Values.deploymentMode "persistent" }}
 apiVersion: v1
 kind: Service
 metadata:
@@ -21,4 +20,3 @@ spec:
     {{- end }}
   selector:
     {{- include "devcontainer.labels" . | nindent 4 }}
-{{- end }}