Summary

Task Reference: [MYMR-205]

Adopts Biome 2.4.15 as the project's code formatter. ESLint stays in charge of linting; Biome's linter and assist are disabled to keep the change surgical and preserve eslint-config-next rules.

Commits on this branch (will be squashed):

1. chore: add biome formatter scaffolding — @biomejs/biome@2.4.15 dev dep, biome.jsonc, bun run format / format:check scripts, CI Format check step.
2. chore: apply biome format baseline — one-shot reformat of 231 files matching the existing style (2-space, double quote, semicolons always, trailing commas all, line width 80, LF).
3. chore: enable jsonc parser flags and set vcs default branch — json.parser.allowComments/allowTrailingCommas so tsconfig.json and other JSONC files parse cleanly, plus vcs.defaultBranch="main" for future biome format --changed --since=main workflows. Also removes the prematurely-added .git-blame-ignore-revs (see below).

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Documentation

Testing

• Tested locally with bun run dev
• Linting passes (bun run lint)
• Typecheck passes (bun run typecheck)
• Formatter passes (bun run format:check)

Notes for reviewer

• Review commits individually. The baseline diff is large (231 files, ~7800 line changes) but every change is whitespace / quote / wrap. Reviewing commit 1 (scaffolding) and commit 3 (config tune-up) is where the actual decisions live.
• Biome config enables css.parser.tailwindDirectives for Tailwind v4 @theme support in app/globals.css.
• Excluded from formatting: node_modules/, .next/, out/, build/, dist/, coverage/, .vercel/, *.tsbuildinfo, next-env.d.ts, bun.lock, migrations/, drizzle/.
• .git-blame-ignore-revs is intentionally NOT in this PR. Squash-merge produces a new SHA that does not exist on any branch until after the merge lands. A follow-up PR will create the file pointing at the real squash SHA on main.
• Optional follow-ups deferred per MYMR-205 scope: editor format-on-save configs (.vscode, .zed), husky + lint-staged pre-commit hook, CONTRIBUTING.md documentation.