fix: resolve CJS type declarations via exports require condition

[ben-vargas]

Problem

Both publint and @arethetypeswrong/cli flag the package exports: exports["."] had a single "types": "./dist/index.d.ts" (ESM declarations) alongside "require": "./dist/index.cjs". TypeScript consumers using CommonJS under node16/nodenext module resolution got "Masquerading as ESM" (FalseESM) — the types claim ESM but the runtime file is CJS.

The build (tsup) already emits ./dist/index.d.cts; it just wasn't wired up.

Fix

Split the exports["."] conditions so each runtime format resolves matching declarations:

".": {
  "import": { "types": "./dist/index.d.ts", "default": "./dist/index.js" },
  "require": { "types": "./dist/index.d.cts", "default": "./dist/index.cjs" }
}

./package.json export and top-level main/module/types (node10 resolution) unchanged. No build changes needed.

Also adds a CHANGELOG entry under the unreleased 3.0.5 section.

Verification

• npm run build — emits index.js, index.cjs, index.d.ts, index.d.cts
• npx publint — All good!
• npx @arethetypeswrong/cli --pack . — No problems found, all green including node16-from-CJS (previously 🥸 FalseESM)
• Smoke test: installed the packed tarball in a temp dir; both require() and import load the full API, and tsc --module node16 --moduleResolution node16 --strict --skipLibCheck passes for both .cts and .mts consumers
• npm run ci — typecheck, lint, 358/358 tests pass

Note (pre-existing, out of scope)

With skipLibCheck: false, node16 CJS consumers still hit TS1479 inside dist/index.d.cts because it imports types from @opencode-ai/sdk/v2, which is ESM-only upstream (no require condition; that's also why index.cjs loads it via dynamic import() at runtime). Invisible to standard configs (skipLibCheck: true) and not fixable in this package's exports.