feat(tui): add markdown rendering support and toggle command

- Introduce new `owlen-markdown` crate that converts Markdown strings to `ratatui::Text` with headings, lists, bold/italic, and inline code.
- Add `render_markdown` config option (default true) and expose it via `app.render_markdown_enabled()`.
- Implement `:markdown [on|off]` command to toggle markdown rendering.
- Update help overlay to document the new markdown toggle.
- Adjust UI rendering to conditionally apply markdown styling based on the markdown flag and code mode.
- Wire the new crate into `owlen-tui` Cargo.toml.

crates/owlen-core/src/sandbox.rs

@@ -185,14 +185,20 @@ impl SandboxedProcess {
         if let Ok(output) = output {
             let version_str = String::from_utf8_lossy(&output.stdout);
             // Parse version like "bubblewrap 0.11.0" or "0.11.0"
-            if let Some(version_part) = version_str.split_whitespace().last()
-                && let Some((major, rest)) = version_part.split_once('.')
-                && let Some((minor, _patch)) = rest.split_once('.')
-                && let (Ok(maj), Ok(min)) = (major.parse::<u32>(), minor.parse::<u32>())
-            {
-                // --rlimit-as was added in 0.12.0
-                return maj > 0 || (maj == 0 && min >= 12);
-            }
+            return version_str
+                .split_whitespace()
+                .last()
+                .and_then(|part| {
+                    part.split_once('.').and_then(|(major, rest)| {
+                        rest.split_once('.').and_then(|(minor, _)| {
+                            let maj = major.parse::<u32>().ok()?;
+                            let min = minor.parse::<u32>().ok()?;
+                            Some((maj, min))
+                        })
+                    })
+                })
+                .map(|(maj, min)| maj > 0 || (maj == 0 && min >= 12))
+                .unwrap_or(false);
         }
 
         // If we can't determine the version, assume it doesn't support it (safer default)