Release 0.30.0: your own toolbar, hover colours, theme-matched website pictures - #84

- The Settings gear is drawn in the primary colour like Screenshot and Theme beside it, so
  the three icons on the right match (orange in the Ember themes).
- The Open in slicer / Open in FreeCAD button gets the hover effect too. The button itself is
  filled with the primary colour, so there the tile turns solid white with the symbol in a
  deeper shade of that colour (tool_icon(on_primary=True)). Its icon is now redrawn on a theme
  switch as well, since the hover picture depends on the theme.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Nothing the program uses changes:
- slicer.find_creality_print: a leftover from 0.1/0.2, when Creality Print was the only
  slicer. Detection goes through find_slicer()/detect_installed() for every slicer,
  Creality Print included; migrate_settings() for old settings stays.
- print_check._hex_rgb, scene.set_plate_axes (main_window sets show_plate_axes itself),
  theme.theme_icon (the old half-circle icon, replaced by the palette tile),
  theme.apply_dark_theme, units.from_display and updates.notes_since (replaced by
  whats_new): never called. The What's new link and version-range tests now use whats_new.
- An unused import (QSpinBox), two unused variables, and tools/panel_width_probe.py, a
  one-off measuring script nothing refers to.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

…ttons look

A new Settings page, Toolbar (also ☰ -> Customize toolbar…, or right-click the toolbar):
- Home, Open, Check, View, Measure, Screenshot, Theme and Settings can be hidden. The menu,
  Open in slicer, Export STL, Plate and Fit are always shown. The order never changes: a hidden
  button only leaves the toolbar (Plate stays the first view button, Fit the last).
- Nothing gets lost: hidden buttons keep their keys, and the ☰ menu now also has Check, View
  and Measure (as switches, with their keys) and the Theme menu.
- Look: the view buttons as "Plate (P)" (default), "Plate", "P" or icon only, and optionally
  joined into one connected group (Iso ... Right join it too while the view cube is off).
- Every change shows right away, in the window and in a picture of the toolbar on the page;
  OK keeps it, Cancel goes back, Reset to defaults shows everything again.

New settings: toolbar_hidden, toolbar_labels, toolbar_joined (ui/toolbar_prefs.py). The
actions keep their full names (menus, tooltips); the toolbar shows their icon text. Docs:
"Toolbar buttons" in README and the guide (en, ar, nl). New texts are drafts in every language.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

# Conflicts:
#	src/printview3d/ui/theme.py

…e pictures

- Version 0.30.0; changelog in English, Arabic and Dutch, with a link from What's new to the
  Toolbar buttons section of the website (in the user's language).
- Arabic and Dutch: the new Settings -> Toolbar texts reviewed.
- Website and README: "New in 0.30", a "Your toolbar" row in the features, and a short GIF of
  Settings -> Toolbar (docs/assets/toolbar-settings.gif, 245 KB; tools/make_toolbar_gif.py).
- Website pictures follow the website's theme: every screenshot also in Light and Ember
  (name--light.webp, name--ember.webp; 4 MB in all), shown by tools/mkdocs_theme_images.py and
  extra.css. tools/make_screenshots.py and tools/make_clips.py got --theme. The Dark
  screenshots are made again (Settings now has the Toolbar page); dialog buttons are shown
  without the Linux desktop's icons, as on Windows and macOS.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>