Select Color: colour book folders, app-style view toggles, load button by the book list

- Colour books now come from folders, like AutoCAD's Color Book
  Locations: Options > Files lists them (add, open, remove); by default
  one color_books folder in the config directory. The Color Books tab
  shows the built-in books plus every .acb in those folders; Load copies
  the chosen file into the first folder. Web: session only, as before.
- Grid/list buttons use the app's toggle style (light accent, its text
  colour for the icon, same corners as inactive).
- Color Books: the load button sits right of the book list; the search
  box keeps its start over the page strip and runs to the end.
- Translations for the two new Options strings in all 22 locales.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_013rGmDUNr1hUf4zo1X3dak8

src/app/view/modal.rs

@@ -367,6 +367,7 @@ impl OpenCADStudio {
                             }
                         },
                         &self.qnew_template,
+                        &self.color_book_dirs,
                         self.double_click_block_refedit,
                         self.double_click_block_attedit,
                         self.cursor_type,