docs: add Sphinx documentation build and deploy workflow

- Add Gitea Actions workflow to build and deploy docs on push to main
- Generate Sphinx reference documentation for all apps and modules
- Deploy versioned and latest docs via rsync over SSH

docs/Makefile

@@ -0,0 +1,22 @@
+# Minimal Sphinx Makefile.
+SPHINXOPTS    ?=
+SPHINXBUILD   ?= sphinx-build
+SOURCEDIR     = source
+BUILDDIR      = _build
+
+.PHONY: help clean html livehtml Makefile
+
+help:
+	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+
+clean:
+	rm -rf $(BUILDDIR) $(SOURCEDIR)/reference/apps
+
+html:
+	@$(SPHINXBUILD) -M html "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+
+livehtml:
+	sphinx-autobuild "$(SOURCEDIR)" "$(BUILDDIR)/html" $(SPHINXOPTS) $(O)
+
+%: Makefile
+	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)