Add regression tests for inline schema autocompletion

[yamcodes]

Context

Inline schema autocompletion (without the type() helper) has regressed twice now:

• Schema autocompletion no longer works without type helper (0.7.6 → 0.7.7) #522 — first reported in v0.7.7, fixed in v0.7.8 via Fix editor autocomplete for arkenv / createEnv function #531
• Autocompletion still broken in ^0.9.2 (same issue as #522) #790 — regressed again in v0.9.x

Both times the root cause was changes to the createEnv overload signatures in create-env.ts that broke TypeScript's ability to provide string literal suggestions for ArkType DSL values.

Task

Add automated regression tests that catch autocompletion breakage. Options to explore:

• @arktype/attest or similar type-level testing to assert that EnvSchema<T> resolves correctly for inline objects
• dtslint / tsd / expect-type style assertions that verify the parameter type narrows to ArkType's string DSL union
• A simple type-level test that ensures arkenv({ KEY: "..." }) infers the same types as arkenv(type({ KEY: "..." })) — if the types diverge, autocompletion likely broke
• Vitest type testing

The goal is to prevent this from silently regressing a third time.