Day 5 slice: Layer 2 iOS + Android (fast structural checks)

[dadachi]

Summary

Extends Layer 2 runtime validation to iOS and Android with platform-keyed dispatch. Each platform's check mirrors Rails' spirit — "does the project even load?" — with the cheapest command that exercises the whole toolchain without booting servers or building full artifacts.

Signature change

// before
runLayer2({ railsDir: "..." })

// after
runLayer2({ platform: "rails" | "ios" | "android", outDir: "...", timeoutMs? })

Only consumer was the smoke test; updated alongside.

Platform strategies

Platform	Check	What it validates
Rails	mise exec -- bundle check → bundle install (if needed) → bin/rails routes	Gem resolution, whole class graph loads, routes compile
iOS	xcodebuild -list -project <*.xcodeproj>	pbxproj parses, SPM dependency graph resolves
Android	./gradlew --version	Gradle wrapper works, build script parses

Perf on freshly-generated clinic-queue

Platform	Duration	Note
Rails (cold)	24.6s	Full bundle install
Rails (warm)	1.3s	bundle check short-circuits
iOS	2.1s	Includes SPM fetch
Android	0.7s	Wrapper check

What's not in this PR

• Full builds (xcodebuild build, ./gradlew assembleDebug) — next slice. Adds real compile validation but increases runtime to 60-90s+ per platform.
• Judge integration — runJudge still stubs all three layers; wiring Layer 2 into the pipeline is a separate concern.

Test plan

• npm run ci — 7/7 green
• Real Rails Layer 2 → pass: true, exit 0, 24.6s cold / 1.3s warm
• Real iOS Layer 2 → pass: true, exit 0, 2.1s
• Real Android Layer 2 → pass: true, exit 0, 0.7s
• Missing xcodeproj / missing gradle wrapper → pass: false with informative stderrTail