docs: fix wording and responsive utility examples (#42458)

docs: fix wording and responsive utility examples (#42458)

Copy edits across several docs pages: clarify .btn usage and theme classes (button.mdx); correct repeated/awkward 'drawer' phrasing and update responsive breakpoint syntax to the colon form (drawer.mdx); remove duplicated 'drawer' wording and clean navbar responsive copy (navbar.mdx); update Sass guidance from @import to @use/@forward terminology (customize/optimize.mdx); clarify 'modal' → 'modal dialog' and update form validation guidance to use data-bs-validate and :user-invalid (getting-started/approach.mdx); and revise display utility docs to show the new .{breakpoint}:d-{value} syntax with example adjustments (utilities/display.mdx).