refactor(core): let Node decide the config module format

[Hebilicious]

Cleans up the loader change in #69, which worked but did more than it needed to.

packages/cssforge/src/loader.ts no longer walks package.json files, parses them, or guesses the module system from source text. It asks Node for the format Node chose and overrides only commonjs-typescript:

const loaded = nextLoad(url, context);
if (loaded.format !== "commonjs-typescript") return loaded;

return {
	format: "module-typescript",
	source: loaded.source ?? readFileSync(fileURLToPath(parsed), "utf8"),
	shortCircuit: true,
};

That drops packageTypeOf, its cache, and the usesEsmSyntax regex, whose false positive silently switched a CommonJS-authored file to ESM, so 67 lines become 15 and the rule reads as one sentence: TypeScript in the config graph loads as ESM when Node would read it as CommonJS.

Behavior change: a CommonJS-authored .ts module inside a CommonJS package now loads as ESM, matching the documented export default config shape. That is the trade for removing the heuristic, and the changeset says so.

Also adds the review rule to AGENTS.md: a pull request is never merged without an explicit instruction for that pull request, release pull requests included.

Verification: the loader test now covers "type": "commonjs", "type": "module", and an absent type field, and fails when the load hook is removed; cssforge:test, typecheck, format, readme-check, and jsr-dry-run pass; the JSR smoke passes with --require-deno; the example browser suite passes 5/5; and a Vite project built against locally packed 0.8.1 plus the plugin emits the tokens under all three type fields.

[changeset-bot]

🦋 Changeset detected

Latest commit: 5082eda

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@hebilicious/cssforge	Patch

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