Bring back dark mode support with simpler logic

[dkhalife]

• merge storage context into themecontext
• TokenManager -> api util
• reduce themecontext
• lowercase util files
• dead code
• remove Contexts
• remove theme from app
• JoyUI to save in custom storage key
• remove custom ThemeContext
• remove custom ThemeMode
• simplify theme toggles
• apply theme

PR Overview

This PR refactors and simplifies theming by merging storage context into theme context, streamlining theme toggles, and removing unused context code.

• Consolidates theme management and storage logic in src/constants/theme.ts
• Simplifies toggle button components by removing the ThemeContext dependency and relying on direct state and util function updates
• Removes obsolete context and custom theme types and utilizes JoyUI’s CssVarsProvider for theming

Reviewed Changes

File	Description
src/constants/theme.ts	Centralizes theme logic and introduces helper functions for mode handling
src/views/Settings/ThemeToggleButton.tsx	Updates toggle behavior to work purely on component state
src/App.tsx	Removes unused theme code and integrates CssVarsProvider
src/views/Settings/ThemeToggle.tsx	Refactors theme toggle control to remove context dependency
src/utils/dom.ts	Adds applyTheme utility to update the document’s theme data attribute
src/views/Settings/Settings.tsx	Removes ThemeContext usage and simplifies settings view
src/views/Navigation/NavBar.tsx	Strips out ThemeContext consumer and adjusts theme toggle placement
src/contexts/ThemeContext.tsx	Eliminates obsolete theming context

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

src/constants/theme.ts:15

• The function getNextThemeMode does not handle the 'system' theme mode, which could lead to undefined behavior when the current mode is 'system'. Consider adding an explicit case or a default branch to handle this scenario.

export const getNextThemeMode = (currentThemeMode: Mode): Mode => {