feat: expose effort level setting in UI (#269)

Adds `--effort <level>` CLI flag support with a dropdown selector in the config sidebar. Valid options are low, medium, high, xhigh (Opus 4.7 only), and max.

src/lib/commands/slashCommands.ts

@@ -77,6 +77,7 @@ async function changeDirectory(path: string): Promise<void> {
         bare_mode: config.bare_mode ?? false,
         show_clear_context_on_plan_accept: config.show_clear_context_on_plan_accept ?? true,
         custom_model_option: config.custom_model_option || null,
+        effort_level: config.effort_level || null,
       },
     });
 
@@ -164,6 +165,7 @@ async function startNewConversation(): Promise<void> {
         bare_mode: config.bare_mode ?? false,
         show_clear_context_on_plan_accept: config.show_clear_context_on_plan_accept ?? true,
         custom_model_option: config.custom_model_option || null,
+        effort_level: config.effort_level || null,
       },
     });