server should require an executable engine

Bug description

Documents with server: shiny should require that an executable engine is in use.

Steps to reproduce

---
title: "not shiny"
server: shiny
---

Actual behavior

The output from quarto inspect indicates that only the markdown engine is in use.

Expected behavior

quarto inspect should indicate an inconsistency, as the document requires a server but contains no executable code.

Your environment

NA.

Quarto check output

Quarto 1.6.42
[✓] Checking environment information...
      Quarto cache location: /Users/aron/Library/Caches/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.4.0: OK
      Dart Sass version 1.70.0: OK
      Deno version 1.46.3: OK
      Typst version 0.11.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.6.42
      Path: /Users/aron/quarto/quarto-1.6.42-macos/bin

[✓] Checking tools....................OK
      TinyTeX: (not installed)
      Chromium: (not installed)

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /Library/TeX/texbin
      Version: 2024

[✓] Checking basic markdown render....OK

[✓] Checking Python 3 installation....OK
      Version: 3.12.2
      Path: /opt/homebrew/opt/python@3.12/bin/python3.12
      Jupyter: (None)

      Jupyter is not available in this Python installation.
      Install with python3 -m pip install jupyter

[✓] Checking R installation...........OK
      Version: 4.3.3
      Path: /Library/Frameworks/R.framework/Resources
      LibPaths:
        - /Library/Frameworks/R.framework/Versions/4.3-arm64/Resources/library
      knitr: 1.50
      rmarkdown: 2.29

[✓] Checking Knitr engine render......OK