fix(napi): return undefined for missing envs

[wan9chi]

Motivation

Missing env vars requested through @voidzero-dev/vite-task-client need to be exposed as JavaScript undefined, matching the package contract. The napi binding previously returned Rust Option<String> directly, which lets absent values cross the native boundary as null and can break callers that check specifically for undefined.

Changes

• Return Either<String, Undefined> from the napi getEnv binding so absent envs are created as real JavaScript undefined.
• Add an e2e snapshot fixture that verifies a missing runner-served env is observed as undefined through the public client package.
• Add a changelog entry for the user-facing fix.

[wan9chi]

• fix(napi): return undefined for missing envs #508 👈 (View in Graphite)
• main

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[wan9chi]

Merge activity

• Jul 4, 3:55 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Jul 4, 3:56 PM UTC: Graphite rebased this pull request as part of a merge.
• Jul 4, 3:58 PM UTC: @wan9chi merged this pull request with Graphite.