fix: install session sync CLI from npm

[skulidropek]

Closes #235

Summary

• publish @prover-coder-ai/docker-git-session-sync as a public npm CLI package
• install the session sync CLI from npm in generated Dockerfiles for post-push backups
• keep a local Docker build fallback before the first npm publish and for offline rebuilds
• add template and package tarball smoke coverage

Verification

• bun run --cwd packages/docker-git-session-sync typecheck
• bun run --cwd packages/docker-git-session-sync test
• bun run --cwd packages/docker-git-session-sync build
• bun --cwd packages/lib vitest run tests/core/templates.test.ts tests/usecases/prepare-files.test.ts
• bun run --cwd packages/lib typecheck
• bun run --cwd packages/app check
• bun run --cwd packages/app build
• bash scripts/e2e/local-package-cli.sh
• bun run check