✨ Replace CalendarThemeProvider with ThemeData.extensions and unify color palette

[lavigarg-simform]

Description

This PR removes CalendarThemeProvider and CalendarThemeData in favour of
Flutter's standard ThemeData.extensions mechanism, unifying all package color
tokens into a single CalendarViewColors palette (with matching light and
dark sub-palettes).

What changed:

• CalendarThemeProvider and CalendarThemeData are deleted. Calendar themes
  are now injected and read exclusively via ThemeData.extensions.
• A new CalendarViewColors token palette replaces the separate
  LightAppColors/DarkAppColors classes. Each …ViewThemeData seeds its
  .light() and .dark() constructors from the shared palette.
• All five BuildContext theme accessors (context.dayViewColors,
  context.weekViewColors, context.monthViewColors,
  context.multiDayViewColors, context.scheduleViewColors) are now
  brightness-aware: they fall back to .dark() defaults when the ambient
  Theme brightness is dark and no extension is registered (previously always
  fell back to .light()).
• ScheduleViewThemeData is introduced with full light/dark/copyWith/
  lerp/merge support.
• The example app's theme layer is rewritten around a single AppColors
  source-of-truth palette and a new ThemeController (InheritedNotifier)
  for runtime theme-mode switching.

Existing behaviour that changes:
Apps using darkTheme without registering calendar ThemeExtensions will now
receive dark-palette calendar defaults instead of light ones. To preserve
customisations in both modes, register extensions on both theme and
darkTheme — see the updated setup example in doc/documentation.md.

Checklist

• The title of my PR starts with a [Conventional Commit] prefix (fix:, feat:, docs: etc).
• I have followed the [Contributor Guide] when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Migration instructions

1. Remove CalendarThemeProvider

// Before
CalendarThemeProvider(
  themeData: CalendarThemeData(dayViewTheme: ...),
  child: MyApp(),
)

// After — register extensions directly on ThemeData
ThemeData.light().copyWith(
  extensions: [DayViewThemeData.light().copyWith(...)],
)

2. Rename multiDayViewTheme → multiDayViewColors

// Before
context.multiDayViewTheme

// After
context.multiDayViewColors

3. Register extensions on darkTheme too

The theme accessors now honour dark-mode brightness. Any app setting
darkTheme: should register the calendar extensions there as well:

MaterialApp(
  theme: ThemeData.light().copyWith(extensions: [...light extensions...]),
  darkTheme: ThemeData.dark().copyWith(extensions: [...dark extensions...]),
)

Related Issues

None

UI Screenshots

Updated UI for the example app home page in mobile and web view

[Copilot]

Pull request overview

This PR modernizes the package’s theming by removing the custom CalendarThemeProvider / CalendarThemeData layer and switching fully to Flutter’s ThemeData.extensions, while unifying the default color tokens into a single CalendarViewColors palette with light/dark sub-palettes. It also updates the example app to use a single palette source-of-truth and adds runtime theme-mode switching.

Changes:

• Replaced legacy theme provider/data + Light/Dark token classes with ThemeExtension-based theming and a unified CalendarViewColors palette.
• Made BuildContext theme accessors brightness-aware when no extension is registered (light vs dark defaults).
• Reworked the example app’s theming to use AppColors + a ThemeController for ThemeMode switching, and updated docs/changelog for the breaking migration.

Reviewed changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
lib/src/theme/week_view_theme_data.dart	Seed defaults from CalendarViewColors.light/dark instead of legacy token classes.
lib/src/theme/schedule_view_theme_data.dart	Introduces/updates ScheduleView theming with light/dark defaults seeded from unified palette.
lib/src/theme/multi_day_view_theme_data.dart	Seed defaults from CalendarViewColors.light/dark.
lib/src/theme/month_view_theme_data.dart	Seed defaults from unified palette; rename copyWith param to cellHighlightColor.
lib/src/theme/light_app_colors.dart	Removes legacy light token palette class.
lib/src/theme/day_view_theme_data.dart	Seed defaults from CalendarViewColors.light/dark.
lib/src/theme/dark_app_colors.dart	Removes legacy dark token palette class.
lib/src/theme/calendar_view_colors.dart	Adds unified raw design-token palette (light/dark sub-palettes + shared tokens).
lib/src/theme/calendar_theme_data.dart	Removes legacy CalendarThemeData wrapper.
lib/src/schedule_view/schedule_view.dart	Updates docs to describe ThemeData.extensions-based styling.
lib/src/extensions.dart	Makes theme accessors brightness-aware and removes the old multiDayViewTheme accessor extension.
lib/src/calendar_theme_provider.dart	Removes legacy CalendarThemeProvider InheritedWidget.
lib/calendar_view.dart	Updates public exports to drop legacy theming types.
example/lib/widgets/week_view_widget.dart	Simplifies time-slot color logic (removes weekend special-case).
example/lib/widgets/day_view_widget.dart	Migrates example usage from provider-based theme lookup to context.dayViewColors.
example/lib/widgets/calendar_configs.dart	Reworks settings UI to use themed dropdowns + ThemeController ThemeMode selection.
example/lib/theme/theme_controller.dart	Adds ThemeController (InheritedNotifier) to drive runtime ThemeMode switching.
example/lib/theme/dark_app_colors.dart	Removes legacy example dark palette class.
example/lib/theme/app_theme.dart	Rebuilds example ThemeData around AppColors.light/dark and registers calendar ThemeExtensions on both themes.
example/lib/theme/app_theme_extension.dart	Updates example ThemeExtension to seed from AppColors.light/dark instead of a separate dark palette.
example/lib/theme/app_colors.dart	Consolidates example palette into AppColors.light/dark plus shared accent constants.
example/lib/pages/web/web_home_page.dart	Removes old boolean dark-mode callback wiring.
example/lib/pages/mobile/mobile_home_page.dart	Replaces boolean dark-mode toggle with a themed ThemeMode selection dialog.
example/lib/pages/home_page.dart	Removes old theme callback plumbing; pages now rely on ThemeController.
example/lib/main.dart	Rewires app composition to use ThemeController and a stable EventController.
example/lib/l10n/app_es.arb	Updates strings for ThemeMode selection UI (system/light/dark).
example/lib/l10n/app_en.arb	Updates strings for ThemeMode selection UI (system/light/dark).
example/lib/l10n/app_ar.arb	Updates strings for ThemeMode selection UI (system/light/dark).
example/lib/extension.dart	Makes example context.appColors brightness-aware when no extension is registered.
example/lib/constants.dart	Updates constants to reference the new AppColors.light palette values.
doc/documentation.md	Updates theming documentation and adds migration guidance for removed provider/accessors.
CHANGELOG.md	Records breaking theming changes and API renames for the upcoming release.

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