fix: convert markdown headings to bold in show command for Matrix rendering

Element X doesn't style <h2> tags distinctly. Convert ## headings to
**bold** text with a blank line above for consistent rendering across
all Matrix clients.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/chat/commands/show.rs

@@ -34,9 +34,31 @@ pub(super) fn handle_show(ctx: &CommandContext) -> Option<String> {
 
     // `content` comes from the CRDT / content store.  If unavailable, report
     // it rather than silently reading a stale on-disk copy.
-    Some(content.unwrap_or_else(|| {
+    let text = content.unwrap_or_else(|| {
         format!("Story {story_id} found in pipeline but its content is unavailable.")
-    }))
+    });
+
+    // Convert markdown headings to bold text for consistent rendering across
+    // Matrix clients. Element X doesn't style <h2> tags distinctly, but bold
+    // text renders consistently everywhere.
+    let formatted = text
+        .lines()
+        .map(|line| {
+            let trimmed = line.trim_start();
+            if let Some(rest) = trimmed.strip_prefix("### ") {
+                format!("\n**{}**", rest)
+            } else if let Some(rest) = trimmed.strip_prefix("## ") {
+                format!("\n**{}**", rest)
+            } else if let Some(rest) = trimmed.strip_prefix("# ") {
+                format!("\n**{}**", rest)
+            } else {
+                line.to_string()
+            }
+        })
+        .collect::<Vec<_>>()
+        .join("\n");
+
+    Some(formatted)
 }
 
 #[cfg(test)]