Render GH Markdown alerts in Sphinx docs (#4663)

See
https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts

We started using this syntax recently: #4466 #4662

## How to test

See preview:
https://anki-core--4663.org.readthedocs.build/en/4663/windows.html

Author: abdnh

CONTRIBUTORS

@@ -55,7 +55,7 @@ neitrinoweb <github.com/neitrinoweb/>
 Andreas Reis <github.com/nwwt>
 Matt Krump <github.com/mkrump>
 Alexander Presnyakov <flagist0@gmail.com>
-Abdo <abdo@abdnh.net>
+Abdo <github.com/abdnh>
 aplaice <plaice.adam+github@gmail.com>
 phwoo <github.com/phwoo>
 Soren Bjornstad <anki@sorenbjornstad.com>

docs/conf.py

@@ -10,6 +10,7 @@
     "myst_parser",
     "sphinx.ext.intersphinx",
     "autoapi.extension",
+    "click_extra.sphinx",
 ]
 
 source_suffix = {

pyproject.toml

@@ -2,7 +2,7 @@
 name = "anki-dev"
 version = "0.0.0"
 description = "Local-only environment"
-requires-python = ">=3.9"
+requires-python = ">=3.12"
 classifiers = ["Private :: Do Not Upload"]
 
 [dependency-groups]
@@ -32,6 +32,7 @@ docs = [
   "sphinx-book-theme",
   "sphinx-autoapi",
   "sphinx-autobuild>=2024.10.3",
+  "click-extra[sphinx]", # for GitHub alerts
 ]
 
 [tool.uv.workspace]