Show the pace marker on thread details usage limit bars

[wrymn]

Thread details is where you check limits mid-chat before picking the next model or effort. Its bars show "% left" but not whether you're ahead of or behind the window, so you can't tell at a glance if you can afford a more expensive model.

Proposal: show the pace tick the Usage page bars (web and mobile) already have. Fill past the tick means under pace, short of it means you're burning too fast.

Before	After

Two-line implementation: #34269. Is this direction OK?

[wrymn]

Duplicate of #28548, which makes the same change and is the PR being kept. Closing this in favor of it.