[Feature]: Git Changes diff: resizable panes and next/previous-difference navigation across files #211

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

apps/web

Problem or use case

I review agent-made change sets in the Git manager's Changes tab before committing, typically 20–40 files. Today that is very hard:

• The diff of the selected file is shown in a fixed strip about 120 px high, between the changed-files list (about 6 rows) and the Amend Last Commit / commit form. On a 1910×1022 window it shows about 5 code lines at a time.
• The borders between the file list, the diff and the commit form cannot be dragged, and the diff cannot be maximised or opened on its own, so the space cannot be given to the diff.
• Unchanged code is folded ("1 unmodified line", "95 unmodified lines"), which is good, but there is no way to jump to the next or previous change, within a file or across files. The only ways to move are scrolling the 5-line strip or clicking files in the list one by one.

(BiBCode 0.13.0, Windows 11 x64.)

Proposed solution

1. Resizable layout: draggable splitters between the file list, the diff and the commit form, plus a way to collapse the commit form or maximise the diff, or pop it out. The sizes are remembered.
2. Changes-only focus: unchanged lines hidden by default, with a few context lines around each change (as today's folding, with more room).
3. Difference navigation like Beyond Compare: next/previous-difference buttons and keyboard shortcuts (e.g. F7 / Shift+F7 or Alt+↓ / Alt+↑). At the last change of a file, next moves on to the first change of the next file in the list.
4. Optional: a side-by-side view next to the unified view, and an overview bar marking where the changes are in the file.

Why this matters

Reviewing what an agent changed before committing is a core step. With 5 visible lines and no change-to-change navigation, reviewing a 30-file change set is slow and easy to get wrong, so people fall back to an external diff tool.

Smallest useful scope

Draggable splitter between the diff and the commit form, plus next/previous-change navigation across files.

Alternatives considered

Opening the worktree in an external diff tool (Beyond Compare, VS Code). It works, but it leaves BiBCode and loses the line-level stage/discard actions.

Risks or tradeoffs

The commit form must stay reachable when the diff is maximised, e.g. as a collapsible section or a shortcut to focus the summary field.

Examples or references

Beyond Compare (next/previous difference, "show differences only"), VS Code's diff editor (F7 / Shift+F7, inline and side-by-side toggle).