chore: add prettier with format scripts

Prettier config (no semi, single quotes, 100 cols, tailwindcss plugin)
scoped via .prettierignore to frontend code only; markdown, docs, CI
workflows, website/, and src-tauri/ are excluded. Scripts follow the
toolchain split: format/format:check (prettier), format:rust(:check)
(cargo fmt), format:all for both.

.prettierrc

@@ -0,0 +1,14 @@
+{
+  "semi": false,
+  "singleQuote": true,
+  "jsxSingleQuote": false,
+  "trailingComma": "es5",
+  "printWidth": 100,
+  "tabWidth": 2,
+  "useTabs": false,
+  "bracketSpacing": true,
+  "bracketSameLine": false,
+  "arrowParens": "always",
+  "endOfLine": "lf",
+  "plugins": ["prettier-plugin-tailwindcss"]
+}