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/components/ConfigSidebar.svelte

@@ -78,6 +78,7 @@
     task_loop_auto_commit: false,
     task_loop_commit_prefix: "feat",
     task_loop_include_summary: false,
+    effort_level: null,
   });
 
   let showCustomThemeEditor = $state(false);
@@ -716,6 +717,29 @@
         </p>
       </div>
 
+      <!-- Effort Level -->
+      <div class="mb-4">
+        <label class="block text-sm text-[var(--text-primary)] mb-1" for="effort-level"
+          >Effort level</label
+        >
+        <select
+          id="effort-level"
+          bind:value={config.effort_level}
+          class="w-full px-3 py-2 rounded border border-[var(--border-color)] bg-[var(--bg-primary)] text-[var(--text-primary)] text-sm focus:outline-none focus:ring-1 focus:ring-[var(--accent-primary)]"
+        >
+          <option value={null}>Default (CLI decides)</option>
+          <option value="low">Low</option>
+          <option value="medium">Medium</option>
+          <option value="high">High</option>
+          <option value="xhigh">Extra High (Opus 4.7 only)</option>
+          <option value="max">Max</option>
+        </select>
+        <p class="text-xs text-[var(--text-tertiary)] mt-1">
+          Passes <code class="font-mono">--effort</code> to tune speed vs. intelligence. Requires Claude
+          Code v2.1.111+.
+        </p>
+      </div>
+
       <!-- Bare Mode -->
       <div class="mb-4">
         <label class="flex items-center gap-3 cursor-pointer">