refactor(theme): remove custom theme editor and community themes

Remove unused custom theme functionality:
- Delete custom-themes-store.svelte.ts from shared-theme
- Remove ThemeEditor, ColorPicker, ThemeLivePreview components
- Remove CommunityThemeGallery, ThemeCommunityCard components
- Remove ThemeEditorPage, CommunityThemesPage
- Simplify ThemePage to show only built-in themes
- Remove editor and community routes from contacts app
- Update THEMING.md documentation

The built-in theme variants (default, ocean, forest, sunset, etc.)
provide sufficient customization. Custom theme creation was never
fully implemented and added unnecessary complexity.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/shared-theme/src/index.ts

@@ -28,18 +28,6 @@ export type {
 	StartPageConfig,
 	WeekStartDay,
 	GeneralSettings,
-	// Custom & Community Themes Types
-	ThemeColorsInput,
-	CustomTheme,
-	CreateCustomThemeInput,
-	UpdateCustomThemeInput,
-	CommunityTheme,
-	CommunityThemeQuery,
-	PaginatedCommunityThemes,
-	PublishThemeInput,
-	ThemeEditorState,
-	CustomThemesStore,
-	CustomThemesStoreConfig,
 } from './types';
 
 // User Settings Constants
@@ -48,9 +36,6 @@ export { DEFAULT_GLOBAL_SETTINGS, DEFAULT_GENERAL_SETTINGS } from './types';
 // Theme Variant Categories
 export { DEFAULT_THEME_VARIANTS, EXTENDED_THEME_VARIANTS } from './types';
 
-// Custom Theme Constants
-export { MAIN_THEME_COLORS, EXTENDED_THEME_COLORS, THEME_COLOR_LABELS } from './types';
-
 // Constants
 export {
 	THEME_VARIANTS,
@@ -81,9 +66,6 @@ export { createA11yStore } from './a11y-store.svelte';
 // User Settings Store
 export { createUserSettingsStore } from './user-settings-store.svelte';
 
-// Custom Themes Store
-export { createCustomThemesStore } from './custom-themes-store.svelte';
-
 // Utils
 export {
 	isBrowser,