WIP: trailing dot on database-name completions

[rolandwalker]

Description

Distinguish database names from table names in completion menus by a trailing dot on database names (aka schema names).

The dot is informational only, and is not inserted when the completion candidate is selected.

One reason this is a WIP is that the dot still appears on a use statement. It should only appear when database names are mixed with table names.

xref: #1876

Example:

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 .

[rolandwalker]

Closing without further work. The dot feels like visual clutter.