fix(config): emit section and section_value in JSON output for config subcommands (#2990)

`claw config model --output-format json` and all other section subcommands
(`env`, `hooks`, `plugins`) returned identical output with no section field
— the section arg was parsed but discarded (_section parameter).

Fix: render_config_json now:
- Passes section through to handler
- Looks up the section value via runtime_config.get(), converting the
  internal JsonValue to serde_json::Value via render()+parse
- Emits `section` (string) and `section_value` (JSON value or null)
  in the response envelope
- Returns ok:false + error for unsupported section tokens

Test: config_section_json_emits_section_and_value asserts:
- No section field when no section arg
- section + section_value fields present for all known sections
- ok:false + error for unknown section

Pinpoint: ROADMAP #126

rust/crates/rusty-claude-cli/src/main.rs

@@ -6210,7 +6210,7 @@ fn render_config_report(section: Option<&str>) -> Result<String, Box<dyn std::er
 }
 
 fn render_config_json(
-    _section: Option<&str>,
+    section: Option<&str>,
 ) -> Result<serde_json::Value, Box<dyn std::error::Error>> {
     let cwd = env::current_dir()?;
     let loader = ConfigLoader::default_for(&cwd);
@@ -6243,13 +6243,52 @@ fn render_config_json(
         })
         .collect();
 
-    Ok(serde_json::json!({
+    let base = serde_json::json!({
         "kind": "config",
         "cwd": cwd.display().to_string(),
         "loaded_files": loaded_paths.len(),
         "merged_keys": runtime_config.merged().len(),
         "files": files,
-    }))
+    });
+
+    if let Some(section) = section {
+        let section_rendered: Option<String> = match section {
+            "env" => runtime_config.get("env").map(|v| v.render()),
+            "hooks" => runtime_config.get("hooks").map(|v| v.render()),
+            "model" => runtime_config.get("model").map(|v| v.render()),
+            "plugins" => runtime_config
+                .get("plugins")
+                .or_else(|| runtime_config.get("enabledPlugins"))
+                .map(|v| v.render()),
+            other => {
+                return Ok(serde_json::json!({
+                    "kind": "config",
+                    "section": other,
+                    "ok": false,
+                    "error": format!("Unsupported config section '{other}'. Use env, hooks, model, or plugins."),
+                    "cwd": cwd.display().to_string(),
+                    "loaded_files": loaded_paths.len(),
+                    "files": files,
+                }));
+            }
+        };
+        // Parse the rendered JSON string back into serde_json::Value so that
+        // section_value is a real JSON object/array in the envelope, not a quoted string.
+        let section_value: serde_json::Value = section_rendered
+            .as_deref()
+            .and_then(|s| serde_json::from_str(s).ok())
+            .unwrap_or(serde_json::Value::Null);
+        let mut obj = base;
+        let map = obj.as_object_mut().expect("base is object");
+        map.insert(
+            "section".to_string(),
+            serde_json::Value::String(section.to_string()),
+        );
+        map.insert("section_value".to_string(), section_value);
+        return Ok(obj);
+    }
+
+    Ok(base)
 }
 
 fn render_memory_report() -> Result<String, Box<dyn std::error::Error>> {