Add independent Jupyter (.ipynb) presentation output with RISE metadata

[Copilot]

This PR adds a new Jupyter output path so presentations can be exported as .ipynb notebooks suitable for slideshow workflows (including RISE-style metadata).
Implementation follows the existing output architecture while keeping Jupyter output fully separate from RevealJS code.

• New Jupyter output projects

  • Added LiquidVictor.Output.Jupyter (shared Jupyter output types/extensions)
  • Added LiquidVictor.Output.Jupyter.Generator (notebook builder implementing IPresentationBuilder)
  • Added LiquidVictor.Output.Jupyter.Test (focused unit coverage)
  • Registered all new projects in LiquidVictor.sln

• Notebook generation engine (OutputEngineType=JUPYTER)

  • Added DI wiring in LV/ServiceCollectionExtensions to resolve the new engine when OutputEngineType is JUPYTER
  • Engine writes a valid .ipynb document (nbformat: 4, nbformat_minor: 5)
  • Slide deck content is emitted as markdown cells with metadata.slideshow.slide_type
  • Includes notebook-level livereveal metadata (theme/transition/autolaunch)
  • Supports optional title-slide creation via BuilderOptions.BuildTitleSlide
  • Includes presenter notes as separate markdown cells (slide_type: "notes")

• Content handling

  • Text content items render as markdown cell source
  • Image content items render as markdown image links using embedded data URIs
  • Unsupported content types fail fast with NotSupportedException

• Project wiring updates

  • Added Jupyter generator reference to src/LV/LV.csproj
  • README feature list now mentions Jupyter .ipynb export support

Example of the generated notebook structure:

{
  "cells": [
    {
      "cell_type": "markdown",
      "metadata": { "slideshow": { "slide_type": "slide" } },
      "source": ["# First Slide\n", "\n", "Body markdown\n"]
    }
  ],
  "metadata": {
    "livereveal": {
      "autolaunch": false,
      "theme": "Black",
      "transition": "Slide"
    }
  },
  "nbformat": 4,
  "nbformat_minor": 5
}