chore: add prettier + enforce LF line endings

- Add .prettierrc (double quotes, 2-space, trailing comma es5, LF, 100 cols)
- Add .prettierignore (excludes node_modules, .next, server/, lock files)
- Add .editorconfig (LF + per-language indent rules for all editors)
- Expand .gitattributes to cover all text file types with eol=lf
- Add prettier@^3.5.3 devDep at workspace root with format/format:check scripts
- Add format/format:check scripts to web/package.json

web/package.json

@@ -5,7 +5,9 @@
   "scripts": {
     "dev": "next dev --turbopack",
     "build": "next build",
-    "start": "next start"
+    "start": "next start",
+    "format": "prettier --write .",
+    "format:check": "prettier --check ."
   },
   "dependencies": {
     "next": "15.5.15",