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>

scripts/startapp.sh

@@ -4,13 +4,7 @@ set -e
 
 echo "=== Starting Dev Container ==="
 
-# Check if we're in serverless mode
-if [[ "$SERVERLESS_MODE" == "true" ]]; then
-    echo "Serverless mode detected, using serverless startup script..."
-    exec /usr/local/bin/serverless-startapp
-fi
-
-# Traditional mode - initialize repository
+# Initialize repository
 /usr/local/bin/init-repo
 
 # Get workspace directory