feat: add web interface, REST API server, and monorepo package restructuring

[johnksterling]

Summary

Introduces a web interface and local REST API server (jazz-tools serve) for interactive harmonic analysis and companion score previewing, while reorganizing the Go codebase into idiomatic cmd/jazz-tools and internal/jazz packages.

Changes Made

• Project Layout Modernization:
  • Reorganized 23 domain files into internal/jazz/ with package declaration package jazz.
  • Moved CLI entry point to cmd/jazz-tools/main.go.
  • Updated .github/workflows/ci.yml build step to target ./cmd/jazz-tools.
• HTTP Server & REST API (internal/server/):
  • Added jazz-tools serve [--port 8080] [--host 0.0.0.0] command.
  • Added POST /api/analyze to parse iReal Pro URLs, HTML playlists, or MusicXML files into structured harmonic journey and Berklee device data.
  • Added POST /api/companion/xml for companion sheet MusicXML generation.
  • Added POST /api/companion/pdf for LilyPond print PDF compilation.
  • Added GET /api/samples (bundled tunes: Waltz For Debby, Jordu) and GET /api/health.
• Interactive React SPA (web/):
  • Built with React 19, TypeScript, Vite, Tailwind CSS, and OpenSheetMusicDisplay (OSMD).
  • Live SVG score rendering of voice-led 3rds and 7ths.
  • Visual harmonic journey badge timeline with Berklee palette colors.
  • Identified Berklee harmonic devices list (ii-V, subV, secondary dominants, turnarounds).
  • Measure-by-measure chord table with voice-leading details.
  • Single-binary distribution via Go embed.FS in web/embed.go (no Node.js required at runtime).
• Documentation:
  • Updated README.md with jazz-tools serve walkthrough and build instructions.

Verification & Testing

• go test -v -race ./... passes
• go vet ./... passes
• gofmt -l . clean
• LilyPond PDF compilation verified
• CLI smoke tests (--help, analyze, serve) verified