Add SystemPromptEntry type to capture system prompt, model, and provider
when sharing sessions via /share command. The entry is inserted into the
JSONL after the header and displayed in the web viewer as a collapsible
section with a model badge.
- Add SystemPromptEntry with Content, Model, and Provider fields
- Capture current system prompt and model at share time
- Display in web viewer with collapsible UI and model badge
- Update documentation for /share command
Ed Zynda