Remove all theme switching, creation, and management functionality
from the app — backend (Rust theme module, Tauri commands, menu items,
startup tasks, vault seeding), frontend (useThemeManager, ThemePropertyEditor,
themeSchema, command palette Appearance group, settings panel appearance
section, isDarkTheme prop chain), mock data, and all related tests.
Editor styling via theme.json/EditorTheme.css is preserved (not user theming).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
a6b2454184