Remove nested disclosure from command timeline details

[bb-slop-cop]

Human comments

What was wrong

The expanded timeline body mounted a second command disclosure with its own state initialized to collapsed, so opening the row left the command under a separate two-line clamp. The independent reproduction and root-cause report is https://get-bb.github.io/reports/issues/3152.html.

What changed

The command detail is now a non-interactive fully visible block inside the already-expanded row. It retains the existing maximum-height overflow behavior for exceptionally long commands. A focused React regression covers the outer-row interaction and verifies that the command has no nested disclosure or clamp.

How you verified

• Before the production change, the focused test failed because the rendered command remained a button with aria-expanded="false" and -webkit-line-clamp: 2.
• After the change, the focused test passed.
• pnpm exec turbo run test typecheck lint --filter=@bb/app passed: 481 test files, 3,923 passing tests, 4 skipped, and all 6 Turbo tasks successful.
• git diff --check origin/main passed.
• The change covers 2 files and 60 text lines: 46 additions and 14 deletions, with no binary changes.

Fixes #3152

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