Draft: fix #714 packaged SDK export validation

[andikrueger]

Closes #714

Summary

This fixes the packaged CLI/SDK FSStorageProvider mismatch by making tarball creation rebuild fresh artifacts and by tightening packaging/export coverage.

Root cause

FSStorageProvider is exported in source, but npm pack could reuse stale dist/ output when package tarballs were created from package directories. That allowed a tarball to carry outdated SDK build artifacts even though the current TypeScript source exported FSStorageProvider correctly.

What changed

• added prepack scripts to packages/squad-sdk and packages/squad-cli so npm pack rebuilds fresh package artifacts
• updated test/cli-packaging-smoke.test.ts to rely on npm pack rebuilding the tarballs instead of conditionally reusing existing dist/
• extended test/package-exports.test.ts to assert FSStorageProvider is exported from both @bradygaster/squad-sdk and @bradygaster/squad-sdk/storage
• extended the packaging smoke test to verify those packaged exports inside the installed tarball

Validation

• npm run build -w packages/squad-sdk
• npm run build -w packages/squad-cli
• npx vitest run test\\package-exports.test.ts test\\cli-packaging-smoke.test.ts

Status

Implementation is complete, but I am leaving this PR in draft state for now.

[diberry]

🔄 Ralph PR status

Check	Status
Mergeable	✅ Clean
Draft	Yes
Base	dev
Commits	1
Changed files	4
Closes	#714

Implementation complete per author. Draft intentional — author left it for review. Clean and minimal (46 adds / 17 dels). Ready to undraft when author/reviewer decide.