Add documentation index URL to inline help

[rolandwalker]

Description

Show docs URL in footer after inline help.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

Findings (ordered by severity)

1. Potential encoding/terminal rendering issue
   mycli/packages/special/main.py:169 introduces a non‑ASCII em dash in the status string (Docs index — ...). In some terminals (especially Windows w/ non‑UTF‑8 codepages), this can display as ? or break alignment. Consider using ASCII - or -- to avoid encoding regressions.

2. Missing test coverage
   There’s no test asserting the inline help footer/status output. A small test around show_help()’s SQLResult.status would lock in the behavior and prevent regressions (e.g., verify it contains DOCS_URL).

No security issues found.

Open questions / assumptions
I didn’t find any existing tests for help output in this repo; if they live elsewhere, point me to them and I’ll re‑evaluate.

Suggestions (if you want to follow up)

1. Add a targeted unit test for show_help() status content.
2. Replace the em dash with ASCII to avoid encoding edge cases.