Render plaintext task list items for markdown files (#26186)

- The library that's being used for org-mode, [doesn't render the status
of list items](https://github.com/niklasfasching/go-org/issues/63).
- Add a modified version of the proposed CSS snippet to still display
the status for the list items. The alternative was parsing HTML and
transforming it, which is too complicated for this small task.
- Resolves https://codeberg.org/Codeberg/Community/issues/1099

(cherry picked from commit 9753c7e4b8)

Refs: https://codeberg.org/forgejo/forgejo/pulls/1071

Co-authored-by: Gusted <postmaster@gusted.xyz>

web_src/css/markup/content.css

@@ -556,3 +556,26 @@
   border-top-left-radius: 0 !important;
   border-top-right-radius: 0 !important;
 }
+
+.file-view.markup.orgmode li.unchecked::before {
+  content: "[ ] ";
+}
+
+.file-view.markup.orgmode li.checked::before {
+  content: "[x] ";
+}
+
+.file-view.markup.orgmode li.indeterminate::before {
+  content: "[-] ";
+}
+
+/* This is only needed for <p> because they are literally acting as paragraphs,
+ * and thus having an ::before on the same line would force the paragraph to
+ * move to the next line. This can be avoided by an inline-block display that
+ * avoids that property while still having the other properties of the block
+ * display. */
+.file-view.markup.orgmode li.unchecked > p,
+.file-view.markup.orgmode li.checked > p,
+.file-view.markup.orgmode li.indeterminate > p {
+  display: inline-block;
+}