fix(sidebar): rest the footer on the composer's baseline

[haitaopanhq]

Outcome

The sidebar footer (设置 / 语言 / 主题) and the composer card are the shell's two bottom blocks, sitting side by side across the window — but nothing kept them aligned. Reported as "对话框UI 最低高度 和左侧边栏那个三设置 高度 不对齐".

They now share a baseline and a height.

Measured before

	Sidebar footer	Composer card (minimum)
Block height	1 + 6 + 40 + 6 + 40 + 6 + 40 = 139	176 − 8 − 8 − 8 = 152
Bottom edge	paneBottom − 4	paneBottom − 16
Top edge	paneBottom − 143	paneBottom − 168

A 25pt step between the footer's divider and the card's top edge, and a 12pt step at the bottom. Two unrelated components would be fine; two blocks spanning the same row read as broken.

Fix

Only the sidebar side moves — the composer's minimum height is unchanged.

• The footer adds 12pt below; the sidebar pane's own 4pt padding makes up the composer's 16pt.
• The divider gap widens until the block reaches the composer card's 152pt.

The numbers are named and derived (sidebarFooterBlockHeight is composed from its parts) rather than inlined as magic constants.

What keeps it aligned

test/features/app/sidebar_footer_baseline_test.dart asserts the footer block equals the composer's minimum card height, and that the two bottom insets match. These blocks live in unrelated widgets, so nothing else would notice if one of them moved.

One test guards the derivation rather than the result: the arithmetic assumes assistantComposerBaseHeightCompactInternal wins over assistantWorkspaceMinLowerPaneHeightInternal. If that ever flips, the other tests would be comparing against a number the layout no longer uses — so that assumption is asserted explicitly and fails first.

Verification

• flutter analyze --no-pub → clean
• flutter test → 568 passed, 6 failed. The 6 are the pre-existing mobile baseline, unchanged from main.
• Confirmed visually in a release build (window-targeted capture): the footer's last row and the composer card end on the same line.

Migration / rollback

Presentation only. Straight revert.

🤖 Generated with Claude Code