feat(styles): remove Material-UI dependency for React 19 compatibility

- Remove @material-ui/styles dependency and replace with custom JSS implementation
- Add comprehensive test suite with Vitest (52 tests, 100% coverage)
- Add TSDoc documentation for all exported APIs
- Update README with comprehensive documentation
- Add utility modules for JSS setup, class name generation, and sheet management
- Enhance StylesProvider with seed-based scope isolation
- Improve TypeScript types with better inference

BREAKING CHANGE: Removed @material-ui/styles dependency

Signed-off-by: Odin Thomas Rochmann <odin.rochmann@gmail.com>

Author: odinr

.changeset/react-styles-remove-material-ui.md

@@ -0,0 +1,40 @@
+---
+"@equinor/fusion-react-styles": major
+---
+
+Remove `@material-ui/styles` dependency and replace with custom JSS-based implementation for React 19 compatibility.
+
+ref: https://github.com/equinor/fusion-framework/issues/3698
+
+### Breaking Changes
+
+- Removed `@material-ui/styles` dependency - replaced with direct JSS integration
+- All Material-UI v4 styling APIs are now implemented internally
+- No API changes - existing code should work without modifications
+
+### Added
+
+- Custom `makeStyles` implementation using JSS directly
+- Custom `StylesProvider` with enhanced scope isolation via seed prefixes
+- Custom `ThemeProvider` with React 19 compatibility
+- Comprehensive test suite with Vitest (52 tests, 100% statement coverage)
+- Utility modules in `src/utils/`:
+  - `jss-setup.ts` - JSS instance configuration
+  - `class-name-generator.ts` - Class name generation logic
+  - `sheet-manager.ts` - Stylesheet caching and management
+  - `contexts.ts` - React context definitions
+- TSDoc documentation for all exported APIs
+- Updated README with comprehensive documentation
+
+### Changed
+
+- Package now uses JSS directly instead of Material-UI wrapper
+- Improved TypeScript types with better inference
+- Enhanced class name isolation for micro-frontend scenarios
+
+### Technical Details
+
+- React 19 compatible (tested with React ^18 || ^19)
+- Uses JSS v10 with all necessary plugins
+- Maintains backward compatibility with existing API surface
+- Full test coverage with Vitest and React Testing Library