Adjust form spacing without submit buttons

[lovasoa]

Motivation

• Prevent forms rendered without submit/reset buttons (for example when auto_submit is used) from leaving extra bottom spacing in the layout.
• Record the UI fix in the changelog rather than (only) the README as intended.

Description

• Change sqlpage/templates/form.handlebars to conditionally apply mb-0 on the fieldset when no submit/reset buttons will be rendered by using the existing Handlebars condition around validate, auto_submit, and reset.
• Update CHANGELOG.md to add an unreleased entry: Fix: forms without submit or reset buttons no longer keep extra bottom spacing.
• A small README documentation line was also touched during the edits, but the primary record of the change is in CHANGELOG.md as requested.

Testing

• Ran cargo test, which failed because the build script could not download external frontend assets due to the environment network being unreachable; no further automated tests completed.

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Codex Task