Add regression tests for parent task link behavior and bump to v1.6.6

[Copilot]

Issue reports parent tasks with links incorrectly auto-check when all direct children complete, even if linked page has incomplete tasks. Investigation confirms current logic correctly handles this:

const childrenComplete = t.children.every((c) => c.completed);
const linksComplete = t.linkChildrenComplete ?? true;
const newVal = childrenComplete && linksComplete;  // Both must be true

Parent only checks when BOTH direct children AND linked page tasks are complete.

Changes

• Added 3 regression tests covering parent task + link + children scenarios
• Added test fixtures: pageA.md, pageB.md, pageA-complete.md
• Bumped version to 1.6.6 per instructions

Test Coverage

1. Parent with incomplete linked page + complete children → remains unchecked ✓
2. Parent with complete linked page + complete children → becomes checked ✓
3. Parent with incomplete children (any link state) → remains unchecked ✓

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Bug: if all the child tasks are completed but their parent linked to page with incomplete tasks</issue_title>
<issue_description>If we have:

...
- [ ] [[pageB]]
 - [x] child A
 - [ ] child B
...

and

...
- [ ] task
...

and child B set checked follows - [x] [[pageB]], but expected to remain unchecked</issue_description>

<agent_instructions>Increment patch version</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Bug: if all the child tasks are completed but their parent linked to page with incomplete tasks #25

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