Seed a hinted and an unhinted code block

The dev server now shows both highlighting paths: a Rust block marked by
its source, and a Python block left to detection.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/seed_dev_db.rs

@@ -131,9 +131,25 @@ fn body_html(title: &str, words: i64) -> String {
             html.push_str("<blockquote><p>A pull quote that the author would rather you remembered than the rest.</p></blockquote>");
         }
         if index == 7 {
-            html.push_str(
+            // One block the source marked as Rust, one it left for detection.
-                "<pre><code>fn main() {\n    println!(\"hello, reader\");\n}</code></pre>",
+            html.push_str(concat!(
-            );
+                "<pre data-lang=\"rust\"><code>/// Greets whoever is reading.\n",
+                "fn main() {\n",
+                "    let reader: &amp;str = \"reader\";\n",
+                "    for n in 0..3 {\n",
+                "        println!(\"hello, {reader} #{n}\"); // three times\n",
+                "    }\n",
+                "}</code></pre>",
+                "<pre><code>import json\n\n",
+                "def load(path: str) -&gt; dict:\n",
+                "    \"\"\"Read a JSON config, or an empty one.\"\"\"\n",
+                "    try:\n",
+                "        with open(path) as f:\n",
+                "            return json.load(f)\n",
+                "    except FileNotFoundError:\n",
+                "        return {}  # first run\n",
+                "</code></pre>",
+            ));
         }
         html.push_str("<p>Paragraph ");
         html.push_str(&(index + 1).to_string());