yoda: phase 2 — customizable toolbar (settings toggles per button)

Phase 1 shipped a fixed 6-button toolbar. Phase 2 moves visibility to
the config so users pick which buttons appear.

Config (config.rs):
- new ToolbarItems struct (CosmicConfigEntry) with one bool per button
- Config.toolbar: ToolbarItems, default = 'minimal 6' set from phase 1
  (new_folder, rename, delete, cut, copy, paste) + 5 extras off
  (new_file, reload, toggle_show_hidden, open_terminal, location_up)

Rendering (view()):
- iterate through self.config.toolbar fields in fixed logical order
  (location → create/edit → clipboard → view toggles)
- dividers inserted only between non-empty groups
- whole toolbar hidden if every button is off (no empty container)

Settings page (settings()):
- new 'Toolbar' section with one toggler per button, wired through
  Message::SetToolbar(ToolbarItems) which persists via config_set!

i18n (en + fr):
- added 'toolbar' + 'parent-directory' strings
- reused existing new-folder / new-file / rename / delete / cut / copy /
  paste / reload-folder / show-hidden-files / open-in-terminal

All actions dispatch through Action::message so keybindings and toolbar
share one code path.

i18n/en/cosmic_files.ftl

@@ -139,6 +139,8 @@ open-with = Open with
 owner = Owner
 group = Group
 other = Other
+toolbar = Toolbar
+parent-directory = Parent directory
 mixed = Mixed
 ### Mode 0
 none = None

i18n/fr/cosmic_files.ftl

@@ -131,6 +131,8 @@ open-with = Ouvrir avec
 owner = Propriétaire
 group = Groupe
 other = Autre
+toolbar = Barre d'outils
+parent-directory = Dossier parent
 
 ### Mode 0