Commit dialog: optional tree view for changed files #30143

Problem

The commit dialog lists changed files as one flat list of full paths. When a change touches many files in a few folders, the list gets long and repetitive, e.g. src/app/blog/[slug]/page.tsx, src/app/blog/[slug]/layout.tsx, src/app/blog/page.tsx. That makes it hard to scan what's being committed. Picking a subset in Edit mode also means ticking files one at a time, even when you want to leave out a whole folder.

Chat and the diff panel already show changed files as a folder tree. The commit dialog is the only place that doesn't.

Proposal

Add a list/tree toggle to the Files header of the commit dialog, next to Edit:

• List stays the default, so the existing behaviour doesn't change. The choice is remembered on that device.
• Tree view groups files by folder. Each folder shows its total +/- count and can be collapsed. Clicking a file still opens it in your editor, the same as in list view.
• In Edit mode, folders get a checkbox. It includes or excludes every file under that folder, and shows a partial state when only some are included.
• The toggle only appears when at least one changed file is inside a folder. Otherwise both views would look the same.

Scope

• Web and desktop only. The tree reuses the same tree builder as the changed-files view in chat.
• What gets committed doesn't change: the dialog still sends the same list of selected files. No server, contract or provider changes.
• Mobile's commit sheet isn't included. I'm happy to follow up there if you want both clients to match.

Prior work I checked

• feat: add selective file staging to commit dialog #872 added selective file staging (the checkboxes).
• fix(web): show filenames when commit dialog paths overflow #6392 fixed long paths being truncated.
• feat: commit dialog refresh #2295 was a closed commit dialog redesign that didn't cover a tree view.
• Stage and unstage files from the Diff panel #22260 proposes staging from the Diff panel and having the commit dialog preselect staged files. It's about which files are selected, not how they're laid out.
• Add compact and panel-only modes for changed files in chat #15104 asked for display modes for the changed-files tree in chat.

None of these propose a tree view in the commit dialog.

I have a working implementation on a branch and can open a PR with before/after screenshots if this direction is OK.