[ThemeProvider] Fix callback dependencies and add onThemeChange callback

[ravisuhag]

Summary

ThemeProvider is a custom theme management system with light/dark mode, localStorage persistence, and system preference detection. Has TypeScript safety issues, stale closure bugs, and obsolete CSS.

Improvements

2. Fix missing useCallback dependencies

• setTheme callback (line 125) is missing storageKey in dependency array — can cause stale closure bugs
• handleMediaQuery callback (line 137) is missing enableSystem dependency

3. Fix invalid JavaScript string generation (line 278)

val construction uses name + "|| ''" which creates syntactically invalid JavaScript in the injected script.

5. Add onThemeChange callback

No event hook for applications that need to react to theme changes.

Moved to Cross-Cutting Issues

The following items have been moved to cross-cutting issues that address them across all components:

• Replace hardcoded CSS values with design tokens (Replace hardcoded CSS values with design tokens #672)
• TypeScript strictness (TypeScript strictness: eliminate any, @ts-ignore, and export prop types #675)
• Clean up deprecated code (Clean up deprecated code, unused CSS, and legacy patterns #682)

Files

• packages/raystack/raystack/components/theme-provider/