docs: comprehensive update for new values format and template names

- Fix CLAUDE.md: update Docker build example from antigravity to devcontainer
- Fix README.md stale value references throughout:
  - ide → ide.type, ssh → ssh.enabled
  - happyServerUrl → happy.serverUrl (and all happy.* values)
  - secureConnection → display.secureConnection
  - userId/groupId → user.id/user.groupId
  - mcpSidecars.* → mcp.sidecars.*
- Remove GitHub MCP sidecar from custom config example (discontinued)
- Fix YAML indentation in MCP config examples
- Fix storage mount path from /home to /config
- Fix Happy state directory from /home/user/.happy to /config/userdata/.happy

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>

CLAUDE.md

@@ -20,7 +20,7 @@ The stack is primarily **Bash scripts + YAML** — there is no Node.js package,
 ```bash
 make build                              # Build Docker image
 make build REGISTRY=ghcr.io/myuser IMAGE_TAG=v1.0  # Custom registry/tag
-docker build -t ghcr.io/cpfarhood/antigravity:latest .  # Direct build
+docker build -t ghcr.io/cpfarhood/devcontainer:latest .  # Direct build
 ```
 
 ### Running Locally