Include status footer in paged output

[rolandwalker]

Description

• Create a new postamble property in SQLResult representing nontabular footer output.
• Refer to SQLResult properties directly more often, eliding temporary variables.
• Convert some old-style SQLResult() constructors in the tests to named parameters.

Motivation: the status property to a SQLResult is not included in the paged output. This was noticeable in the output of the status command, which includes a non-tabular footer which is more naturally part of the paged output.

This suggests a few other changes, such as recasting SQLResult.title as SQLResult.preamble. The trailing line in #1628 would more naturally be a postamble than a status.

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

1. mycli/main.py:1007-1012 drops warning.postamble by passing None. If SHOW WARNINGS ever returns a postamble, it will be silently lost in the watch loop. Consider passing warning.postamble to keep behavior consistent with other format_output calls.

Missing Tests / Edge Cases

1. No test asserts that SQLResult.postamble is appended after formatted output (and thus included in paged output). A focused test around format_output or the status command output would lock in the new behavior.

No security issues spotted in the changes.