Code formatting with Prettier

Description

Set up, advise on, and review Prettier formatting — config files and options, .prettierignore, overrides per file type, plugins (prettier-plugin-tailwindcss, organize-imports, etc.), editor format-on-save, ESLint integration (eslint-config-prettier, not eslint-plugin-prettier), CI checks (--check), pre-commit hooks (lint-staged), monorepos, and v2→v3 changes. Use whenever a .prettierrc/prettier.config.* exists, prettier is in package.json, the user asks to "format the code", fix "Prettier and ESLint fighting", sort Tailwind classes, add a format check to CI, or explains formatting diffs nobody intended.