feat: Phase 2.0 - Server-Sent Events (SSE) Implementation

[apenlor]

Phase 2.0: Server-Sent Events (SSE)

This pull request marks the completion of Phase 2.0, which introduces server-to-client streaming and the GraalVM native executable. All work has been completed, including server-side implementation, containerization, frontend development, robust benchmarking, and final documentation.

Summary of Key Deliverables

• SSE Endpoint: A new reactive endpoint at GET /stream/ticker is implemented in TickerResource.java, streaming JSON payloads every second.
• GraalVM Native Build: A multi-stage Dockerfile.native is added to produce a minimal, secure, and fast-starting GraalVM native executable.
• Side-by-Side Orchestration: The docker-compose.yml is updated to run both server-jvm and server-native services concurrently for direct comparison.
• Frontend Refactoring: The demo-client has been architecturally refactored into a feature-based structure with a central navigation hub, and a new SSE demo page has been added to visualize the streams from both backends.
• Robust Benchmarking Suite:
  • A new SSE benchmark is introduced using a custom-built k6 binary with the xk6-sse extension for accurate, native streaming tests.
  • All benchmark runner scripts (rest_benchmark.sh, sse_benchmark.sh, measure-startup.sh) are standardized to accept a logical service name (server-jvm or server-native) and use a reliable, shared Docker network for communication.
• Architectural Refinements:
  • The Dockerfile.jvm is updated with an explicit ENTRYPOINT to ensure it is a portable, correctly configured artifact.
• Documentation: The project's READMEs are updated to the "index" and "per-phase" model, with the v2.0-sse README now being complete and accurate.

Next Steps

Upon merging this PR, the v2.0-sse tag will be created to freeze this state, and the README.md on the main branch will be updated to its "index" role.