refactor: rename template helpers from antigravity to devcontainer

Rename all Helm template helper functions from antigravity.* to
devcontainer.* to match the actual chart name. Also update Chart.yaml
description to remove "Antigravity" branding.

Renamed helpers:
- antigravity.fullname → devcontainer.fullname
- antigravity.pvcName → devcontainer.pvcName
- antigravity.envSecretName → devcontainer.envSecretName
- antigravity.labels → devcontainer.labels
- antigravity.smartResources → devcontainer.smartResources
- antigravity.smartDefaults → devcontainer.smartDefaults
- antigravity.mcpDefaults → devcontainer.mcpDefaults

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/templates/rbac.yaml

@@ -1,7 +1,7 @@
 {{- $access := .Values.clusterAccess | default "none" }}
-{{- $name   := include "antigravity.fullname" . }}
+{{- $name   := include "devcontainer.fullname" . }}
 {{- $ns     := .Release.Namespace }}
-{{- $labels := include "antigravity.labels" . }}
+{{- $labels := include "devcontainer.labels" . }}
 
 {{- if ne $access "none" }}
 ---