feat(pkgmgr,cli): support scriptgo add, direct file execution, and scg alias

[phamtanminhtien]

Summary

This PR implements three major features and usability enhancements for ScriptGo:

1. scriptgo add Package Manager Command:

   • Supports adding dependencies, devDependencies (-D, --dev), optionalDependencies (-O, --optional), and peerDependencies (--peer).
   • Supports exact version pinning with -E / --exact.
   • Supports offline installation (--offline) against cached packages.
   • Resolves package specs (pkg, pkg@version, pkg@tag, @scope/pkg) via npm registry or workspace packages.
   • Updates package.json with formatting and key order preservation, followed by updating scriptgo.lock and installing packages into node_modules.
   • Features transactional rollback of package.json and scriptgo.lock if any installation step fails.

2. Direct CLI Execution:

   • Users can directly run files without prefixing run:
     • scriptgo file.ts
     • scriptgo -e "console.log('hello')"
     • scriptgo --eval "code"
   • Preserves all flags and arguments passed after the source target.

3. scg Alias:

   • scg is interchangeable with scriptgo.
   • Dynamic program name detection in CLI usage/help output (os.Args[0]).
   • Added cmd/scg delegator binary and updated Makefile to symlink scg -> scriptgo.

4. Architecture & Refactoring:

   • Adhered strictly to AGENTS.md line length guidelines (< 500-650 lines per file):
     • Split binary linking into internal/pkgmgr/bins.go from install.go.
     • Split handleEmit into cmd/scriptgo/emit_cmd.go and handleCoverage into cmd/scriptgo/coverage_cmd.go from main.go.
   • Comprehensive test suites in internal/pkgmgr/add_test.go, cmd/scriptgo/add_test.go, and cmd/scriptgo/main_test.go.
   • Synchronized documentation in CHANGELOG.md, docs/package-manager-architecture.md, docs/roadmap.md, and docs/typescript-parity-report.md.

Verification

• go test -count=1 ./... (All packages pass 100%)
• go test -count=1 ./internal/typescriptgo/...
• go build ./cmd/scriptgo & go build ./cmd/scg