Keep browser-safari builds dry-run safe

[RasputinKaiser]

browser-safari build currently goes straight into host Apple/Xcode tooling, which makes dry-run validation unsafe on machines without Xcode and makes the build path harder to inspect.\n\nProposed fix:\n- emit a dry-run Safari package plan under the target outDir\n- keep dry-run builds side-effect free with respect to Xcode tooling\n- execute converter/archive commands through argv arrays instead of shell-joined command strings in the build path\n- cover the dry-run plan with a focused target test

[Robertg761]

Implemented in PR #185: #185

Summary:

• browser-safari dry-run builds now write safari-package-plan.json before any Xcode checks
• dry-runs are side-effect free with respect to Xcode and Safari converter tooling
• live converter/archive build calls now use argv-based shared exec helper
• focused tests cover the dry-run package plan

Verification:

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