v0.1.2: Preferences page, About page, full icon set, redesigned edit form

- Rework the add/edit form onto a generic, catalog-driven field model
  (JobFieldCatalog + JobEditModel), replacing the old hand-written
  ApplicationEditDialog with ApplicationEditPage
- Add a Preferences page (reachable from the hamburger menu) with a
  KColorSchemeManager-backed color scheme switcher
- Add an About page reading from KAboutData
- Ship a full hicolor icon set (16-128px + scalable) via ecm_install_icons
  instead of a single flat SVG
- Restyle the edit form after KDE System Settings' Audio page:
  Kirigami.ListSectionHeader per category, flat separated rows, no card
  borders
- Explicitly declare Kirigami/KirigamiAddons/ColorScheme as CMake
  dependencies instead of relying on the QML import scanner alone
- Add KDEClangFormat/KDEGitCommitHooks, a CMakePresets.json, and a
  REUSE + clang-format lint CI workflow
- Reformat SPDX headers to include copyright, remove debug screenshot
  scaffolding

.gitignore

@@ -8,3 +8,5 @@
 # Editor / misc
 *.user
 *.autosave
+# Generated by ECM's KDEClangFormat module
+/.clang-format