feat: add YAML syntax highlighting with Prism.js

Add Prism.js (core + YAML grammar, ~9.4 KB) for syntax-highlighted
YAML output in the MCP Apps viewer. Tools returning Kubernetes resource
YAML now render with color-coded keys, strings, numbers, and comments.

- YamlView component with Prism.highlight() and useMemo
- looksLikeYaml() heuristic for Kubernetes resource detection
- Custom theme CSS using light-dark() for host theme integration
- Prism.manual = true to prevent auto-highlighting

Signed-off-by: Marc Nuri <marc@marcnuri.com>

Author: manusa