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/session.rs

@@ -53,8 +53,8 @@ fn extract_resource_content(value: &Value) -> Option<String> {
         Value::Array(items) => {
             let mut segments = Vec::new();
             for item in items {
-                if let Some(segment) = extract_resource_content(item)
-                    && !segment.is_empty()
+                if let Some(segment) =
+                    extract_resource_content(item).filter(|segment| !segment.is_empty())
                 {
                     segments.push(segment);
                 }
@@ -69,17 +69,19 @@ fn extract_resource_content(value: &Value) -> Option<String> {
             const PREFERRED_FIELDS: [&str; 6] =
                 ["content", "contents", "text", "value", "body", "data"];
             for key in PREFERRED_FIELDS.iter() {
-                if let Some(inner) = map.get(*key)
-                    && let Some(text) = extract_resource_content(inner)
-                    && !text.is_empty()
+                if let Some(text) = map
+                    .get(*key)
+                    .and_then(extract_resource_content)
+                    .filter(|text| !text.is_empty())
                 {
                     return Some(text);
                 }
             }
 
-            if let Some(inner) = map.get("chunks")
-                && let Some(text) = extract_resource_content(inner)
-                && !text.is_empty()
+            if let Some(text) = map
+                .get("chunks")
+                .and_then(extract_resource_content)
+                .filter(|text| !text.is_empty())
             {
                 return Some(text);
             }
@@ -566,9 +568,10 @@ impl SessionController {
             .expect("Consent manager mutex poisoned");
         consent.grant_consent(tool_name, data_types, endpoints);
 
-        if let Some(vault) = &self.vault
-            && let Err(e) = consent.persist_to_vault(vault)
-        {
+        let Some(vault) = &self.vault else {
+            return;
+        };
+        if let Err(e) = consent.persist_to_vault(vault) {
             eprintln!("Warning: Failed to persist consent to vault: {}", e);
         }
     }
@@ -588,10 +591,13 @@ impl SessionController {
         consent.grant_consent_with_scope(tool_name, data_types, endpoints, scope);
 
         // Only persist to vault for permanent consent
-        if is_permanent
-            && let Some(vault) = &self.vault
-            && let Err(e) = consent.persist_to_vault(vault)
-        {
+        if !is_permanent {
+            return;
+        }
+        let Some(vault) = &self.vault else {
+            return;
+        };
+        if let Err(e) = consent.persist_to_vault(vault) {
             eprintln!("Warning: Failed to persist consent to vault: {}", e);
         }
     }