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/deployment.yaml

@@ -1,4 +1,3 @@
-{{- if eq .Values.deploymentMode "persistent" }}
 apiVersion: apps/v1
 kind: Deployment
 metadata:
@@ -84,6 +83,10 @@ spec:
             - name: GITHUB_REPO
               value: {{ .Values.githubRepo | quote }}
             {{- end }}
+            {{- if .Values.githubRepos }}
+            - name: GITHUB_REPOS
+              value: {{ join "," .Values.githubRepos | quote }}
+            {{- end }}
           envFrom:
             - secretRef:
                 name: {{ include "devcontainer.envSecretName" . }}
@@ -305,4 +308,3 @@ spec:
         - name: userhome
           persistentVolumeClaim:
             claimName: {{ include "devcontainer.pvcName" . }}
-{{- end }}