Add markdown rendering for LLM output

This commit introduces a new module `analyze::render` to handle the
rendering of Markdown content produced by the LLM into safe HTML.

The LLM output now includes a custom `==text==` highlighting convention
to indicate sections that require doctor review due to potential
transcription errors or incomplete information. This highlighting is
converted into `<mark>` tags in the final HTML.

To ensure security, all LLM-generated Markdown is first HTML-escaped.
This prevents any malicious HTML or script injection from being executed
in the browser. Only the custom `<mark>` tags are preserved as
functional HTML elements.

The process is as follows:
1.  The raw Markdown from the LLM is processed.
2.  All HTML special characters (`<`, `>`, `&`, `"`, `'`) are escaped.
3.  The `==text==` highlights are replaced with `<mark>text</mark>`.
4.  The resulting string is parsed as Markdown by `pulldown-cmark`.
5.  The parsed Markdown is converted to HTML, which is then safe to
    inject into the Askama template using the `|safe` filter.

The `Cargo.toml` and `Cargo.lock` files have been updated to include the
`pulldown-cmark` dependency. The `document.html` template has been
modified to use a `div` with the class `doc-content` instead of a `pre`
tag, allowing the rendered HTML to be displayed correctly. The
`handle_document_view` function now calls the new `md_to_html` rendering
function.

server/src/routes/case_actions.rs

@@ -114,9 +114,10 @@ pub async fn handle_document_view(
         }
     };
 
-    let content = read_document(&case_dir)
+    let md = read_document(&case_dir)
         .await
         .ok_or_else(|| AppError::NotFound("Noch kein Dokument erzeugt".into()))?;
+    let content = crate::analyze::render::md_to_html(&md);
 
     DocumentTemplate { case_id, content }
     .render()