chore: extend biome to all supported files and enforce formatting in CI

[Bilb]

Replaces #31, which added Prettier for this. Biome 2.1.2 formats JSON and CSS natively, so broadening its includes covers 121 of the files a second formatter would have — leaving only README.md and two YAML files uncovered. Not worth a second config to keep in lockstep.

Problem

Two gaps:

1. biome.json had "includes": ["./**/*.ts", "./**/*.tsx"], so next.config.js, tailwind.config.js, knip.config.js, tsconfig.json and styles/globals.css were formatted by nothing.
2. The Lint workflow ran biome lint, which checks lint rules but not formatting. Nothing enforced format anywhere.

There was also an editor symptom: with no repo-level formatter pinned, a contributor whose global VSCode settings point at the Prettier extension gets Prettier's defaults on save, which disagree with biome.json on printWidth (80 vs 100), trailingComma (all vs es5) and embedded-CSS reformatting inside styled.* templates. On pages/pro.tsx that was a 345-line diff on every save.

Changes

biome.json — includes broadened to **, with vcs.useIgnoreFile enabled so build outputs come from .gitignore rather than a hand-maintained exclusion list. ignoreUnknown: true skips the types Biome has no formatter for (md, yaml, images, fonts).

locales/ stays excluded: they're Crowdin exports and differ only by a missing trailing newline, so formatting them would fail CI on every sync. contentful/export.json is a generated CLI dump.

css.formatter.quoteStyle is set to single — Biome defaults CSS to double quotes, which would have churned every url() and font-family in globals.css against the existing convention.

.vscode/settings.json (committed, with a .gitignore negation) pins biomejs.biome as the formatter for js/ts/json/css. Workspace settings beat user settings, so this fixes format-on-save without anyone editing their global config. .vscode/extensions.json recommends the extension.

Workflow — formatting is checked in a separate step with if: always(), not chained onto the lint step. See below.

package.json — one new script, "format:check": "biome format". No new dependency.

Note: the lint step will show red

biome lint already fails on main with 12 errors and has since the workflow was added — run 33366786839 failed on the merge of #30, and the PR that introduced it failed too. The gate has never passed.

Those are pre-existing and unrelated to formatting (noExplicitAny across services/, noNonNullAssertion, noDangerouslySetInnerHtml, noExcessiveCognitiveComplexity, unreachable code in lib/proBackend.ts). They involve real code decisions, so they belong in a separate PR.

This is why the format check is a separate step: chained as biome lint && biome format, the always-failing lint would short-circuit and the format check would silently never run. Split, Check formatting passes while the lint step stays red for the pre-existing reasons.

Broadening includes does not make that worse — error count is still exactly 12, unchanged from main. It adds 4 warnings on next.config.js (unused vars/params), which don't fail the build.

Verification

• pnpm run format:check passes
• biome lint reports 12 errors, identical to main
• next.config.js, tailwind.config.js, postcss.config.js still require() to the same shape; tsc --showConfig still resolves 109 files
• Diff is formatting-only. pages/[slug].tsx is a missing semicolon (there's also a stray console.log(forbiddenWords) on line 46 that predates this and is left alone).

[Bilb]

Removed console.log(forbiddenWords) entirely in 6be470f rather than keeping it formatted — it was a debug leftover.

The other console.log calls in that file are deliberate build-progress output, so I left them.

This does mean the PR is no longer strictly formatting-only. pages/[slug].tsx now shows a two-line deletion instead of a semicolon fix.