Configure CSS as generated asset, not committed to git

- Added public/style.css to .gitignore
- Removed style.css from git tracking (git rm --cached)
- Enhanced package.json scripts for better CSS workflow:
  - postinstall: Auto-builds CSS on npm install
  - build-css:dev: Development build with source maps
  - start: Now builds CSS before starting server
  - dev: Builds CSS before development mode
- Updated README with CSS development documentation
- Explains SCSS organization and build process
- Documents all CSS-related npm scripts

Benefits:
✅ Cleaner repository (no generated files)
✅ Prevents merge conflicts in generated CSS
✅ Automatic CSS generation on new machine setup
✅ Source of truth is SCSS files only
✅ Consistent build process across environments

package.json

@@ -4,14 +4,16 @@
   "description": "Great Lakes Ice Report - Community-driven winter road conditions tracker for Michigan",
   "main": "server.js",
   "scripts": {
-    "start": "node server.js",
-    "dev": "nodemon server.js",
+    "start": "npm run build && node server.js",
+    "dev": "npm run build-css && nodemon server.js",
     "build-css": "sass src/scss/main.scss public/style.css --style=compressed",
-    "watch-css": "sass src/scss/main.scss public/style.css --watch",
+    "build-css:dev": "sass src/scss/main.scss public/style.css --style=expanded --source-map",
+    "watch-css": "sass src/scss/main.scss public/style.css --watch --style=expanded --source-map",
     "dev-with-css": "concurrently \"npm run watch-css\" \"npm run dev\"",
     "build": "npm run build-css",
     "test": "jest --runInBand --forceExit",
-    "test:coverage": "jest --coverage"
+    "test:coverage": "jest --coverage",
+    "postinstall": "npm run build-css"
   },
   "dependencies": {
     "cors": "^2.8.5",