build(docs): the Windows site does not publish docs/linux, docs/macos or docs/dev

mkdocs builds docs_dir: docs, which now also holds docs/linux, docs/macos (each with its own
index.md, README.md and cli/ pages) and docs/dev. Without a change they were all built into
the Windows site (692 files instead of the Windows ones) and 250 warnings appeared for their
links to sources outside docs/. exclude_docs lists /linux/, /macos/ and /dev/; the nav is
not touched.

Verified: mkdocs 1.6.1 with material 9.7.6 and mkdocs-macros 1.3.9 (a nix python env):
`mkdocs build --strict` passes with the change; the file set of the site is exactly the one
of the build without the change minus linux/, macos/ and dev/, and the other files are
byte-identical (search index and sitemap differ because they listed the extra pages).

mkdocs.yml

@@ -5,6 +5,12 @@ site_description: The Tiling Window Manager for Windows
 repo_url: https://github.com/LGUG2Z/komorebi
 repo_name: LGUG2Z/komorebi
 docs_dir: docs
+# docs/ also holds the documentation of the Linux and macOS ports and the developer notes of the
+# consolidation; they are read in the repository, not published on the Windows site
+exclude_docs: |
+  /linux/
+  /macos/
+  /dev/
 theme:
   name: material
   palette: