v1.2.0

This release is about packaging and documentation: the GUI binary is now a
single download that also carries the complete CLI, and the manual is published
as a website.

GUI and CLI binaries

• The GUI binary is now called mhub-gui (previously mhub-webgui) and is a
  superset of the CLI: it dispatches the same commands, so mhub-gui database init works exactly like mhub database init. One download is enough to
  manage MonitorHub from the command line or from a browser.
• The Windows GUI ships as an onedir folder in a versioned zip
  (mhub-gui-<version>-windows.zip) instead of a onefile executable. A onefile
  build of the Streamlit application spends several seconds unpacking itself on
  every start; the folder starts immediately.
• The Linux GUI stays a single self-contained file.
• build_project.py gained an --layout onefile|onedir option and an all
  target. A failed build now stops immediately with an explanation instead of
  continuing to the next target.

Continuous integration

• The GUI artifact is built and published by CI, alongside the CLI.
• Workflow actions were moved to Node 24 runtimes.
• utils/check_actions.py audits the Node runtime every workflow action
  declares, so an action that drops Node 24 support fails the build instead of
  being force-migrated by GitHub.
• A Dependabot configuration keeps the workflow actions current.

Documentation

• The manual is published with MkDocs Material to GitHub Pages:
  https://transparent-systems.github.io/monitorhub/
• The build runs mkdocs build --strict, so a link to a page that does not
  exist fails the build rather than shipping a broken manual.
• New pages cover installation, the first monitor, remote and command profiles,
  the CLI, the database, placeholders and the architecture.
• The README gained a table of contents and links to the published manual.