* feat(coding-agent,tui): support argument-hint frontmatter in prompt templates
Parse argument-hint from prompt template frontmatter and display it
in the autocomplete dropdown description, matching Claude Code's
convention for custom commands.
Frontmatter format:
---
description: Code review
argument-hint: "[file | #PR | PR-URL]"
---
The hint renders in the description column of the autocomplete list:
review [file | #PR | PR-URL] — Code review
Closes#2761
* docs(coding-agent,tui): add argument-hint documentation, tests, and built-in hints
- Document argument-hint frontmatter in prompt-templates.md with <required>/[optional] convention
- Add argument-hint to built-in prompts: pr, is, wr
- Expand tests: required/optional hints, missing hints, empty hints, special characters
- Add changelog entries for coding-agent and tui
When OAuth refresh fails during model discovery, getApiKey() now returns
undefined instead of throwing. This allows the app to start and fall back
to other providers, so the user can /login to re-authenticate.
fixes#498
