mobile-expo should emit EAS dry-run plans

[RasputinKaiser]

The mobile-expo target currently logs the intended EAS build/update/submit command and returns a placeholder artifact path. Dry-run builds and ships should leave behind an inspectable EAS plan so callers can validate the platform, profile, channel, project directory, and command without invoking EAS or requiring Expo credentials.

Real builds should also invoke EAS through argv args instead of shell strings and capture build metadata into a concrete artifact.

[Robertg761]

Implemented in PR #179: #179

Summary:

• dry-run mobile-expo builds now write expo-eas-build.json with provider, appId, version, platform, profile, channel, projectDir, and the resolved EAS argv command
• real builds/ships now invoke eas with argv arrays and EXPO_TOKEN from the vault
• dry-run ships return the resolved update/submit command in metadata

Verification:

• pnpm exec vitest run packages/targets/mobile-expo/src/index.test.ts
• pnpm --filter @profullstack/sh1pt-target-mobile-expo typecheck
• pnpm --filter @profullstack/sh1pt typecheck
• git diff --check