feat: add notification sounds (#44)

### Explanation

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### Issue

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### Attestations

- [ ] I have read and agree to the [Code of Conduct](https://docs.nhcarrigan.com/community/coc/)
- [ ] I have read and agree to the [Community Guidelines](https://docs.nhcarrigan.com/community/guide/).
- [ ] My contribution complies with the [Contributor Covenant](https://docs.nhcarrigan.com/dev/covenant/).

### Dependencies

- [ ] I have pinned the dependencies to a specific patch version.

### Style

- [ ] I have run the linter and resolved any errors.
- [ ] My pull request uses an appropriate title, matching the conventional commit standards.
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### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
- [ ] My contribution modifies existing code, and I have updated the tests to reflect these changes.
- [ ] All new and existing tests pass locally with my changes.
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Reviewed-on: #44
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src/lib/components/ConfigSidebar.svelte

@@ -11,6 +11,8 @@
     theme: "dark",
     greeting_enabled: true,
     greeting_custom_prompt: null,
+    notifications_enabled: true,
+    notification_volume: 0.7,
   });
 
   let isOpen = $state(false);
@@ -394,6 +396,51 @@
       </div>
     </section>
 
+    <!-- Notifications Section -->
+    <section class="mb-6">
+      <h3 class="text-sm font-medium text-[var(--accent-primary)] uppercase tracking-wider mb-3">
+        Notifications
+      </h3>
+
+      <!-- Enable/Disable Notifications -->
+      <div class="mb-4">
+        <label class="flex items-center gap-3 cursor-pointer">
+          <input
+            type="checkbox"
+            bind:checked={config.notifications_enabled}
+            class="w-4 h-4 text-[var(--accent-primary)] bg-[var(--bg-primary)] border-[var(--border-color)] rounded focus:ring-[var(--accent-primary)] focus:ring-2"
+          />
+          <span class="text-sm text-gray-300">Enable sound notifications</span>
+        </label>
+      </div>
+
+      <!-- Volume Control -->
+      <div class="mb-4">
+        <label for="notification-volume" class="block text-sm text-gray-400 mb-2">
+          Notification Volume
+        </label>
+        <div class="flex items-center gap-3">
+          <input
+            id="notification-volume"
+            type="range"
+            bind:value={config.notification_volume}
+            min="0"
+            max="1"
+            step="0.1"
+            disabled={!config.notifications_enabled}
+            class="flex-1 h-2 bg-[var(--bg-primary)] rounded-lg appearance-none cursor-pointer disabled:opacity-50"
+          />
+          <span class="text-sm text-gray-300 w-12 text-right">
+            {Math.round(config.notification_volume * 100)}%
+          </span>
+        </div>
+      </div>
+
+      <div class="text-xs text-gray-500">
+        Sound notifications will play when I complete tasks, encounter errors, or need permissions.
+      </div>
+    </section>
+
     <!-- Save Button -->
     <div class="sticky bottom-0 pt-4 pb-2 bg-[var(--bg-secondary)]">
       <button
@@ -406,3 +453,34 @@
     </div>
   </div>
 </aside>
+
+<style>
+  /* Custom range input styling */
+  input[type="range"]::-webkit-slider-thumb {
+    appearance: none;
+    width: 16px;
+    height: 16px;
+    background: var(--accent-primary);
+    border-radius: 50%;
+    cursor: pointer;
+  }
+
+  input[type="range"]::-moz-range-thumb {
+    width: 16px;
+    height: 16px;
+    background: var(--accent-primary);
+    border-radius: 50%;
+    cursor: pointer;
+    border: none;
+  }
+
+  input[type="range"]:disabled::-webkit-slider-thumb {
+    background: var(--text-tertiary);
+    cursor: not-allowed;
+  }
+
+  input[type="range"]:disabled::-moz-range-thumb {
+    background: var(--text-tertiary);
+    cursor: not-allowed;
+  }
+</style>