fix(deps): externalize unresolvable bare deps with skipNodeModulesBundle

[m2na7]

Description

deps.skipNodeModulesBundle: true is documented as "Skip bundling all node_modules dependencies", but a bare dependency the resolver can't resolve is bundled instead of externalized.

This happens for a dependency published without an exports field on a non-node platform: the resolver doesn't fall back to the legacy main/types fields, so this.resolve(...) returns null. In externalStrategy (src/features/deps.ts) the skipNodeModulesBundle branch was gated on resolved being truthy, so a null resolution fell through to return false and the bare import got bundled.

It's most visible in the dts build, where a types-only dependency ends up inlined into the emitted .d.ts instead of being kept as an external import:

Before

//#region node_modules/my-dep/index.d.ts
interface Foo { a: number; }
//#endregion
export type { Foo };

After

import { Foo } from "my-dep";
export type { Foo };

The fix externalizes the bare specifier in this case too — skipNodeModulesBundle should never bundle a node_modules import whether or not it resolves. Absolute paths and # subpath imports are left untouched, and the change is fully scoped to skipNodeModulesBundle, so default resolution and the existing "Module not found" path (without this option) are unaffected.

Added a regression test in tests/e2e.test.ts (types-only dep + dts: true + platform: 'neutral' + skipNodeModulesBundle: true) that fails without the change and passes with it. pnpm test (full suite), tsc --noEmit, eslint --max-warnings 0, and prettier --check all pass.

Linked Issues

fixes #993

Additional context

The bug reproduces only with the combination in the test: a non-node platform + a dependency lacking an exports field (so the resolver returns null). On a node platform the same dependency resolves via main, so skipNodeModulesBundle already externalizes it correctly.

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commit: 3d783d2