feat: prepare project for cozy-ui migration (#157)

* feat: prepare project for cozy-ui migration

Build Configuration
- Add Stylus support via @rsbuild/plugin-stylus
- Add SVGR support via @rsbuild/plugin-svgr
- Update rsbuild.config.ts with custom configuration
- Add historyApiFallback for SPA routing

ESLint Configuration
- Create .eslintrc.json with react-app configuration
- Remove eslintConfig from package.json

CSS to Stylus Migration
Convert all 5 CSS files to Stylus (.styl) format:
  - src/App.css to src/App.styl
  - src/index.css to src/index.styl
  - src/components/Calendar/Calendar.css to src/components/Calendar/Calendar.styl
  - src/components/Calendar/CustomCalendar.css to src/components/Calendar/CustomCalendar.styl
  - src/components/Menubar/Menubar.css to src/components/Menubar/Menubar.styl
- Update all imports from .css to .styl
- Preserve all styling rules and values

MUI Styling Cleanup
- Replace all MUI sx props with standard style props across 15+ components
- Convert MUI spacing units (mr: 2 to marginRight: 16px)
- Convert MUI shorthand props (p: 2 to padding: 16px, mb: 1 to marginBottom: 8px)
- Remove MUI-specific syntax (&.Mui-checked selectors)
- Maintain exact visual appearance

FullCalendar Fixes
- Comment out problematic CSS rule in CustomCalendar.styl
- Fix display issues with timegrid slot labels

Files Modified
- Config: rsbuild.config.ts, .eslintrc.json, package.json
- Styling: 5 CSS to Stylus conversions, 15+ component sx to style updates
- Components: All components using MUI sx props updated

Development Workflow
- Continue using existing development commands
- Stylus files are now the source of truth for styling
- MUI components work with standard style props
- ESLint uses familiar react-app rules

Dependencies Added
- @rsbuild/plugin-stylus
- @rsbuild/plugin-svgr

src/components/Menubar/Menubar.styl

@@ -0,0 +1,93 @@
+/* Basic reset */
+*
+  margin 0
+  padding 0
+  box-sizing border-box
+
+.twake
+  font-family "Cal Sans"
+  font-weight 400
+  font-size 28.07px
+  line-height 100%
+  letter-spacing 0%
+  text-align center
+  vertical-align middle
+  padding 0.2rem
+
+.calendar-text
+  font-family "Cal Sans"
+  padding 0.2rem
+  font-weight 400
+  font-size 28.07px
+  line-height 100%
+  letter-spacing 0%
+  text-align center
+  vertical-align middle
+  background linear-gradient(180deg, #ffb73d, #f26c32)
+  -webkit-background-clip text
+  -webkit-text-fill-color transparent
+  /* Optional for broader support */
+  background-clip text
+  color transparent
+
+/* Menubar styles */
+.menubar
+  display flex
+  justify-content space-between
+  align-items center
+  padding 0.5rem
+  width 100%
+  z-index 1000
+  height 80px
+  background-color #fff
+
+.menubar-item
+  display flex
+  align-items center
+  width calc(330px - 0.5rem)
+
+.logo
+  padding 0.5rem 1rem
+  font-size 1.5rem
+
+.nav-month
+  padding-right 2px
+  padding-left 2px
+  gap 38px
+
+.day-selector
+  font-weight 100
+  font-size small
+
+.search-bar
+  width 600
+  height 43.88999938964844
+  top 18px
+  left 887px
+
+.app-grid
+  display grid
+  grid-template-columns repeat(3, 1fr)
+  gap 16px
+  padding 16px
+  justify-items center
+  align-items center
+
+.app-grid img
+  width 48px
+  height 48px
+
+.app-grid p
+  margin-top 6px
+  font-size 14px
+  text-align center
+
+.left-menu
+  display flex
+  align-items center
+  justify-content flex-start
+
+.right-menu
+  display flex
+  justify-content flex-end
+  align-items center