feat: add IDE choice — VSCode (default), Google Antigravity, SSH

- Add `ide` Helm value with options: vscode, antigravity, ssh
- Dockerfile: install Google Antigravity via apt and openssh-server
- scripts/startapp.sh: branch on IDE env var to launch the right app
- scripts/cont-init-sshd.sh: start sshd as root in SSH mode, set up
  authorized_keys from SSH_AUTHORIZED_KEYS env var
- chart/templates/deployment.yaml: pass IDE env var, conditional ports
  and probes (HTTP for VNC modes, TCP socket for SSH mode)
- chart/templates/service.yaml: expose port 5800 (VNC) or 22 (SSH)
- chart/values.yaml: add ide field with documentation
- README.md: document IDE choice, fix stale happyHomeDir references
- chart/Chart.yaml: bump to 0.1.5

Closes #10

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

chart/templates/service.yaml

@@ -6,9 +6,16 @@ metadata:
     {{- include "antigravity.labels" . | nindent 4 }}
 spec:
   ports:
+    {{- if eq (.Values.ide | default "vscode") "ssh" }}
+    - port: 22
+      name: ssh
+      protocol: TCP
+      targetPort: ssh
+    {{- else }}
     - port: 5800
       name: vnc-web
       protocol: TCP
       targetPort: vnc-web
+    {{- end }}
   selector:
     {{- include "antigravity.labels" . | nindent 4 }}