feat(files): move files and folders across directories in the stack explorer (#1373)

* feat(files): move files and folders across directories in the stack explorer

Add a cross-directory move to the stack file explorer. Files and folders can
be relocated either through a "Move to..." context-menu item that opens a
folder-picker dialog, or by dragging an entry onto a folder node (or onto the
root area to move it to the stack root).

The backend reuses the existing rename endpoint: renameStackPath now resolves
both ends through the leaf helper, so a symlink moves as the link entry rather
than its target, and it guards against moving a directory into its own subtree.
A cross-filesystem rename surfaces as a clean 409 instead of a 500. Protected
root files (compose / docker-compose / .env) stay put. Moving the open file, or
a folder containing it, deselects the viewer; a move that would discard unsaved
edits is blocked with a clear message.

* fix(files): fold case in move guards and keep the move dialog open on failure

Harden the cross-directory move against case-insensitive filesystems and fix a
dialog dismissal edge:

- Protected root files (compose / docker-compose / .env) were gated by an exact,
  lowercase name match. On a case-insensitive filesystem a request like
  COMPOSE.YAML resolves to the real compose.yaml and slipped past the gate, so a
  protected file could be moved out of the stack root via the API. The gate now
  folds case on case-insensitive platforms; Linux stays case-sensitive, where a
  differently-cased name is a distinct, unprotected file.
- The directory-into-descendant guard compared resolved paths case-sensitively,
  so a source supplied with non-disk casing skipped the guard and fell through to
  an opaque OS error (500) instead of a clean 400. The comparison now folds case
  the same way.
- The move dialog closed after awaiting the move regardless of outcome, so a
  blocked move (unsaved edits) or a failed move dismissed the picker as if it had
  succeeded. The shared handler now reports success and the dialog only closes on
  an actual move.

docs/features/stack-file-explorer.mdx

@@ -21,7 +21,7 @@ The file explorer gives you direct access to everything inside a stack's directo
 
 The **files** shortcut button next to **edit** in the Anatomy header opens the editor and selects the Files tab in one click.
 
-The file explorer is available on every Sencho tier. Read actions (browse, preview, download, inspect permissions) require **stack read** permission, which every signed-in role has by default. Write actions (upload, edit, create, rename, change permissions, delete) require **stack edit** permission on your account.
+The file explorer is available on every Sencho tier. Read actions (browse, preview, download, inspect permissions) require **stack read** permission, which every signed-in role has by default. Write actions (upload, edit, create, rename, move, change permissions, delete) require **stack edit** permission on your account.
 
 ## Layout
 
@@ -116,9 +116,18 @@ When a file is selected, the right pane action bar shows **Download**. Files str
 
 ## Renaming
 
-Right-click any file or folder and choose **Rename**. The dialog accepts a new name following the same rules as creation.
+Right-click any file or folder and choose **Rename**. The dialog accepts a new name following the same rules as creation. Rename keeps the entry in its current folder.
 
-Rename appears only when your account has stack edit permission. The rename is in-place; cross-directory moves are not supported. To move an entry between directories, copy it via the host shell or upload to the new location and delete the original.
+Rename appears only when your account has stack edit permission.
+
+## Moving
+
+Move a file or folder into a different directory in one of two ways:
+
+- **Move to…** Right-click the entry and choose **Move to…**. The dialog shows the stack's folder tree; pick a destination folder (or **Stack root**) and choose **Move**. Destinations that would collide or make no sense (the entry's current folder, a folder inside the entry itself, or a name that is reserved at the stack root) are not selectable.
+- **Drag and drop.** Drag the entry onto a folder in the tree, or onto empty space to move it to the stack root.
+
+Moving requires stack edit permission. The protected stack files (compose / docker-compose / `.env`) at the stack root stay put: the compose CLI reads them from the stack directory, so they are not offered as move sources or root destinations. Moving a file changes only where it lives on disk; it does not redeploy or restart the stack.
 
 ## Permissions (chmod)
 
@@ -164,8 +173,10 @@ When the entry is one of the five protected names, the modal asks you to type th
 
 | Right-click target | Admin entries (with stack edit) | Viewer entries |
 |---|---|---|
-| Folder | New File, New Folder, Rename, Delete | No write entries |
-| File | Rename, Permissions, Delete | Permissions (read-only) |
+| Folder | New File, New Folder, Rename, Move to…, Delete | No write entries |
+| File | Rename, Move to…, Permissions, Delete | Permissions (read-only) |
+
+**Move to…** is absent for the protected stack files (compose / docker-compose / `.env`) at the stack root, which cannot be moved out of the stack directory.
 
 The Permissions dialog opens for everyone; only users with stack edit permission can save changes.
 
@@ -203,6 +214,6 @@ The Permissions dialog opens for everyone; only users with stack edit permission
     Each directory render is capped at 1000 entries to keep the tree responsive. Use the filter input above the tree to narrow the list, or drop into a host shell with `cd` into the stack directory if you need to work with entries past the cap.
   </Accordion>
   <Accordion title="Write controls are missing">
-    Upload, create, rename, chmod save, and delete require **stack edit** permission. Viewer accounts can browse, preview text files, and inspect permissions in read-only mode.
+    Upload, create, rename, move, chmod save, and delete require **stack edit** permission. Viewer accounts can browse, preview text files, and inspect permissions in read-only mode.
   </Accordion>
 </AccordionGroup>