fix(native): report resolver disagreement only under diagnostics

[danfry1]

Fixes #201. Thanks to @doutatsu for the report, and for tracing it to checkResolverAgreement — the analysis was right.

Problem

Every test file printed 'test-renderer' resolves to two different files, along with the same warning for nanoid and Babel's source-map packages. Nothing in those projects loads those packages through Vite: Node requires test-renderer from React Native Testing Library and nanoid from postcss.

The check runs on every Node require and compares the resolved file against the first Vite main field in the package manifest. It has no view of Vite's module graph, so a package only Node ever requires is indistinguishable from one both graphs load. Its suggested remedy didn't help either, because it compares against a fixed field list rather than the project's resolve.mainFields.

Change

• The check now runs under diagnostics only. The silent duplicate-instance failure it was written to surface — a store written through one copy reading back unset through the other — is still worth reporting to someone debugging it.
• The message states that it reports a risk rather than a proven duplicate, and that the comparison uses Vite's default main fields.

Verification

• tests/resolver-agreement-gate.test.ts drives the installed require hook in a subprocess, rather than calling the checker directly, because the gate is at the call site. It asserts silence by default and the warning under diagnostics, and fails without the change.
• In a project matching the report (RN 0.86.3, Vitest 5.0.0, pnpm with node-linker=hoisted, RNTL 14), the warnings are gone by default and still appear with diagnostics: true.
• prepublishOnly passes, plus format:check.