feat(dev-ui): add ui component metadata

[MichaelDoyle]

Adds initial metadata fields for Dev UI, and maps safetySettings and fallback middleware (models) to their respective ui components.

A small schema update to expose StatusNameSchema was also included.

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[gemini-code-assist]

Code Review

This pull request introduces UI-specific schema annotations and metadata keys (GENKIT_UI_METADATA and GENKIT_UI_WIDGETS) to support standard and customized UI widgets, such as model lists and safety settings. It updates various schemas (like Gemini config, fallback options, and retry options) to use these annotations and replaces generic string schemas with StatusNameSchema for status validation. There are no review comments, so I have no feedback to provide.