docs: document code with doxygen, breathe, and sphinx_csharp

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "third-party/sphinx-csharp"]
+	path = third-party/sphinx-csharp
+	url = https://github.com/rogerbarton/sphinx-csharp.git
+	branch = master

.readthedocs.yaml

@@ -8,14 +8,21 @@ version: 2
 
 # Set the version of Python
 build:
-  os: ubuntu-20.04
+  os: ubuntu-22.04
   tools:
-    python: "3.10"
+    python: "3.11"
+  apt_packages:
+    - graphviz  # required to build diagrams
   jobs:
     post_build:
       - rstcheck -r .  # lint rst files
       # - rstfmt --check --diff -w 120 .  # check rst formatting
 
+# submodules required to install sphinx-csharp
+submodules:
+  include: all
+  recursive: true
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   builder: html

.rstcheck.cfg

@@ -3,6 +3,14 @@
 
 [rstcheck]
 ignore_directives =
+    doxygenindex,
+    doxygennamespace,
     include,
+    interface,
     mdinclude,
     todo,
+
+ignore_roles =
+    idxr,
+    interface,
+    prop,

Jellyfin.Plugin.Themerr/Api/ThemerrController.cs

@@ -36,8 +36,9 @@ public class ThemerrController : ControllerBase
 
         /// <summary>
         /// Downloads all Movie theme songs.
+        ///
+        /// A response code of 204 indicates that the download has started successfully.
         /// </summary>
-        /// <response code="204">Theme song download started successfully.</response>
         /// <returns>A <see cref="NoContentResult"/> indicating success.</returns>
         [HttpPost("DownloadMovies")]
         [ProducesResponseType(StatusCodes.Status204NoContent)]