Add prompt templating system with mustache

- Add promptsDir to Paths.hs for $AVA_DATA_ROOT/prompts/
- Create Omni.Agent.Prompts module with:
  - Mustache template loading and rendering
  - Automatic partial resolution via automaticCompile
  - Frontmatter/metadata parsing for list command
- Create omni-agent-prompt CLI for previewing prompts:
  - list: show all available prompts
  - render: render prompt with --var and --json context
- Prompts use .mustache extension for automaticCompile compatibility
- Partials referenced with full extension: {{> shared/memory.mustache}}

0 files changed, 0 insertions, 0 deletions