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

rsbuild.config.ts

@@ -1,10 +1,25 @@
 import { defineConfig } from "@rsbuild/core";
 import { pluginReact } from "@rsbuild/plugin-react";
+import { pluginStylus } from "@rsbuild/plugin-stylus";
+import { pluginSvgr } from "@rsbuild/plugin-svgr";
 
 export default defineConfig({
-  plugins: [pluginReact()],
+  plugins: [pluginReact(), pluginStylus(), pluginSvgr()],
   html: {
     template: "./public/index.html",
   },
-  server: { port: 5000 },
+  server: {
+    port: 5000,
+    historyApiFallback: true,
+  },
+  source: {
+    entry: {
+      index: "./src/index.tsx",
+    },
+  },
+  output: {
+    distPath: {
+      root: "dist",
+    },
+  },
 });