Closed Beta v3 zip shipped with the dev/ directory included

**Status: needs triage** (build process)

## Observation
The MultiplayerClosedBeta-v3.zip distribution of the API mod contains `dev/init.lua` (and its contents differ from the repo's version). The repo's release CI (`.github/workflows/strip-dev.yml`) strips `dev/` from release builds, so the beta zip appears to have been built from a working tree through a path that bypasses that step.

## Impact
Low today — `dev/init.lua` only enables env-var-driven dev auth, and the dev impersonation endpoint 404s against production servers. But it means beta testers are silently running dev-mode clients, and anything added to `dev/` in the future would ship to them unnoticed. Beta builds should go through the same strip step as releases (or include dev tooling deliberately as a documented decision).

.github/workflows/strip-dev.yml から始めて、MultiplayerClosedBeta-v3.zip がどのように生成されたかを追跡し、strip ステップをバイパスしたベータのパッケージングのエントリーポイントを探します。生成されたアーカイブの内容を検証します。ベータビルドで一貫して dev/ が除外されるか、リポジトリがそれを含める意図的な判断を文書化していれば完了です。

索引モデルが issue の本文から書いたものです。