feat: add CI/CD support for 2.0.0-dev builds

Updates GitHub Actions to build development images from serverless feature branch:

## GitHub Actions Updates
- Trigger builds on feature/serverless-* branches
- Add 2.0.0-dev tag for feature/serverless-2.0.0 branch
- New routing proxy build job for serverless features
- Parallel builds: main devcontainer + routing proxy

## Chart Updates
- Default image tag changed to 2.0.0-dev
- Routing proxy tag updated to 2.0.0-dev
- Ready for development testing

## Build Outputs
When pushed to feature/serverless-2.0.0:
- ghcr.io/cpfarhood/devcontainer:2.0.0-dev
- ghcr.io/cpfarhood/devcontainer-routing-proxy:2.0.0-dev

This enables immediate testing of serverless features without manual builds.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

chart/values.yaml

@@ -13,7 +13,7 @@ deploymentMode: persistent  # persistent | dynamic
 # Container image configuration
 image:
   repository: ghcr.io/cpfarhood/devcontainer
-  tag: latest
+  tag: 2.0.0-dev
   pullPolicy: Always
 
 # GitHub repository to clone into /workspace (ignored in dynamic mode - uses URL routing)
@@ -217,7 +217,7 @@ dynamic:
     replicas: 2                    # High availability
     image:
       repository: ghcr.io/cpfarhood/devcontainer-routing-proxy
-      tag: latest
+      tag: 2.0.0-dev
       pullPolicy: Always
 
     resources: