feat(tasks): PR 1.5 — return refreshed subtask + parent from completion

Change complete_subtask_and_check_parent to return
(TaskRow, Option<TaskRow>): the refreshed subtask, plus the parent when
the cascade auto-completed it. Both rows are read inside the same
transaction so the frontend never observes partial state.

Wrap the cmd in a CompleteSubtaskResult { updatedSubtask,
autoCompletedParent } DTO. MicroSteps now applies the refreshed subtask
locally and, when present, calls a new replaceTaskFromDto helper on the
Tasks store so the parent's done/doneAt/badge counts update without a
follow-up list_tasks_cmd round-trip.

Test: complete_subtask_returns_updated_subtask_and_optional_parent
covers both paths (sibling-pending → None, last-sibling → Some(parent)).
All 61 kon-storage tests pass; svelte-check clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/components/MicroSteps.svelte

@@ -2,6 +2,8 @@
   import { invoke } from '@tauri-apps/api/core';
   import { ListTree, Check, Timer, Loader2, ThumbsUp, ThumbsDown, Pencil } from 'lucide-svelte';
   import { profilesStore } from '$lib/stores/profiles.svelte.ts';
+  import { replaceTaskFromDto } from '$lib/stores/page.svelte.js';
+  import type { TaskDto } from '$lib/types/app.ts';
   import SpeakerButton from '$lib/components/SpeakerButton.svelte';
 
   let { parentTaskId, parentTaskText = '', reduceMotion = false } = $props();
@@ -71,9 +73,24 @@
 
   async function checkStep(subtaskId: string) {
     try {
-      await invoke('complete_subtask_cmd', { subtaskId });
+      const result = await invoke<{
+        updatedSubtask: TaskDto;
+        autoCompletedParent: TaskDto | null;
+      }>('complete_subtask_cmd', { subtaskId });
       const idx = subtasks.findIndex(s => s.id === subtaskId);
-      if (idx >= 0) subtasks[idx] = { ...subtasks[idx], done: true };
+      if (idx >= 0) {
+        subtasks[idx] = {
+          ...subtasks[idx],
+          done: result.updatedSubtask.done,
+          text: result.updatedSubtask.text,
+        };
+      }
+      // PR 1.5: when this completion auto-completed the parent, swap the
+      // refreshed parent into the Tasks store so its done state, doneAt,
+      // and badge counts pick up immediately — no full refetch needed.
+      if (result.autoCompletedParent) {
+        replaceTaskFromDto(result.autoCompletedParent);
+      }
       // Phase 6 nudge-bus signal. Any completed step clears the
       // micro-step-idle timer for this parent task — the breakdown
       // is demonstrably getting worked, no nudge needed.