Add list/tree view toggle to the Git tab's Changes list

[vivi7]

Summary

Adds a List / Tree switch to the Changes section of a project's Git tab. List is today's flat view and stays the default. Tree groups the changed files into collapsible folders, like View as Tree in VS Code / Cursor Source Control.

Why

With many changes under a few deep directories (e.g. 30+ untracked files under backend/docs/… and backend/script/…), the flat list repeats the same long prefix on every row and it's hard to see where the changes are. A tree makes the shape of the change obvious and lets you fold away folders you've already looked at.

What it does

• A small segmented control (list / tree icons) in the Changes heading, next to the "N files" count. It uses the same look as the existing .pane-seg control.
• The choice is saved in localStorage (gitChangesView) as one global preference, like the diff mode in the file panel. Unknown values, or storage that throws, fall back to list.
• The tree is built inside each status group (Conflicted, Modified, Added, …), the way VS Code keeps its SCM groups and builds a tree inside each one.
• Folders come before files, sorted naturally and case-insensitively. Chains of folders with a single child collapse into one row (backend/docs/ai-engine), like VS Code's compact folders.
• Folder rows show a chevron, a folder icon and a file count. Clicking one expands or collapses it (aria-expanded), and keyboard focus stays on that folder after the list re-renders. Collapse state lives in memory, per repository.
• File rows in tree mode are a compact single line: status code + file name. The full path (and old → new for renames) plus the staged/unstaged/untracked label move into the tooltip.
• Switching view or folding a folder repaints only the file list. The selected file and its diff pane are left alone: no flash, and no second diff fetch while one is still loading.

Implementation notes

• public/project-git-view.js:
  • pure helpers buildGitChangeTree() and gitTreeRows(), easy to unit-test;
  • createGitFileRow(), shared by both modes, and createGitFolderRow();
  • paintGitChanges() takes { repaintDiff }, so a view switch or folder toggle skips the diff pane;
  • the toggle wiring lives in paintGitRepository().
• public/projects-view.js: new PICONS.tree icon (Lucide list-tree).
• public/style.css: .git-view-toggle / .git-view-btn, .git-folder-row, and .git-file-row.tree. Indentation uses a --depth custom property.
• No changes to main-process code or IPC: the tree is built entirely from the changes array the renderer already receives.

Testing

• New test/project-git-view.test.js (11 tests), which loads the real public/project-git-view.js in a vm context. It covers:
  • nesting and folders-first natural sort;
  • folder compaction, and cases that must not compact;
  • root-level files and renames;
  • collapsed folders hiding their descendants, depth values and file counts;
  • stored-mode fallbacks, including a throwing localStorage;
  • list vs tree render dispatch;
  • a folder click leaving the diff pane untouched and restoring focus.
• npm test: 429/429 pass.
• Manual check in Chromium against the real style.css and project-git-view.js, with a 33-file fixture:
  • both modes, collapse/expand, persistence across reload;
  • keyboard (Tab / Enter / Space);
  • the narrow single-column layout;
  • a file named <b>x-inject-test.sh renders as literal text;
  • no console errors.