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

.prettierrc

@@ -0,0 +1,8 @@
+{
+  "semi": true,
+  "singleQuote": false,
+  "tabWidth": 2,
+  "trailingComma": "es5",
+  "printWidth": 100,
+  "endOfLine": "lf"
+}