feat(browser): add a Tree view mode and align view names with Finder

[spandan11106]

Description

The view switcher named the Miller columns "List", the icon grid "Grid" and the table "Explorer", none of which is what those views are called elsewhere. The labels are now Columns, Icons and List. The BrowserMode variants keep their names, so this is a user-facing rename only.

Adds a fourth presentation, Tree: one vertical pane whose folders expand in place with a disclosure chevron, indented by depth. Its root level mirrors the browser's active column, so selection, inline rename, the item context menu, cut styling and drag and drop behave exactly as they do in List. Rows inside an expanded branch belong to directories the navigation state does not own, so the view lists them through Browser::list_directory and orders them with Browser::sorted_entries — listing budgets, sort order and the hidden-file rule stay in the application layer. Every branch is dropped when the pane's column reloads, so changing the sort or toggling hidden files never leaves a stale listing behind.

Keyboard: →/l expands the focused folder (and activates it when there is nothing to expand), ←/h collapses it, then walks to the parent row, then leaves the directory. ↑/↓ and k/j move through the flattened tree rather than skipping expanded children.

Known limits, both because a row below the root level has no position in the browser's active column: rows inside an expanded branch are not part of the multi-selection the rest of the app acts on, and right-clicking one shows the folder menu rather than the item menu. Clicking, expanding, opening and quick preview all work on them. Worth a follow-up once selection can address entries by location.

Visual evidence

Tree mode, collapsed:

Tree mode, with alpha and alpha/nested expanded:

How to test

1. Build and run Strata over a directory with a few levels of nesting, for example cargo run -- ~/Projects.
2. Open the appearance menu (the toolbar's list icon) and confirm the modes now read Columns, Icons, List, Tree, with the check mark on the mode you are in.
3. Choose Tree, then click the chevron beside a folder, and the chevron beside a folder inside it.
4. Focus a row and press →, ←, ↓ and ↑.
5. Toggle hidden files with Ctrl+H and change the sort from the pane header, both while a branch is expanded.
6. Quit and reopen Strata.

Expected result: folders expand and collapse in place with their children indented one level further and sorted with folders first; arrow keys expand, collapse and move through the flattened tree; hidden files appear and disappear at every level, and a sort change reorders expanded branches too; Strata reopens in Tree mode. Switching to Columns, Icons and List still works as before.

Related issue

Closes #315

[spandan11106]

Sorry the above description does not have proper visuals. Here are some better one.

The name changes for the views :

Tree view does not support group by file types.

screenrecording-2026-09-05_03-52-20.mp4

[l0gicgate]

@spandan11106, keyboard navigation crashes the changes here. Please fix.

[spandan11106]

Fixed in 4cc8bb1.

Root cause: BrowserView::activate_focused held a shared borrow of mode_views while the tree called Browser::activate_in_place, which emits synchronously. The observer then wanted a mutable borrow of the same cell, so it panicked with RefCell already borrowed inside a GTK callback — a extern "C" frame that cannot unwind, so the process aborted rather than unwound. It hit every activation in Tree mode: Enter always, and →/l whenever there was nothing to expand (a file, or an already-expanded folder).

ViewState::handle → mode_views.borrow_mut()   <- panicked here
Browser::emit ← Browser::select ← activate_in_place ← tree::activate_position

The tree now returns what activating a row should do (TreeActivation) instead of doing it, so the caller drops its borrow before the browser runs and emits back into the mode views. Mouse activation goes through the same path, so there is one behaviour to reason about.

Verified by driving tree_step (Next, Expand, Next, Previous, Collapse, Collapse) and activate_focused directly in a running instance in Tree mode: it aborted at the first activation before the change and completes the whole sequence after it. Added unit coverage for the activation intent — root rows resolve to a column position, rows inside an expanded branch to their location.