fix(editor): invalid caret in note-edgeless-block on focus (#14229)

### Problem
●In edgeless mode, when starting to edit, `note-block` exhibits two
types of invalid caret behavior:
(1)**Title Region Misalignment**: Clicking on the title region
incorrectly generates the caret in the first line of the note content,
rather than in the title itself.
(2)**Vanishing Caret at Line End**: When clicking in the empty space
beyond the end of a text section, the caret appears momentarily at the
line's end but disappears immediately.
●The following video demonstrates these issues:


https://github.com/user-attachments/assets/db9c2c50-709f-4d32-912c-0f01841d2024


### Solution
●**Title Click Interception**: Added a check to determine if the click
coordinates fall in the title region. If so, the caret positioning is
now handled by a dedicated logic path. Otherwise, it falls back to the
existing note-content logic as before.
●**Range Normalization**: When the generated `range.startContainer` is
not a `TextNode`, try to find a most appropriate `TextNode` and update
the `range` accordingly.

### After
●The video below shows the behavior after this fix.


https://github.com/user-attachments/assets/b2f70b64-1fc6-4049-8379-8bcf3a488a05



<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Clicking a page block title no longer creates unwanted paragraphs and
reliably focuses the title.
* Paragraph creation now occurs only when needed and focus is applied
only after successful creation.
* Click coordinates are clamped to container bounds to prevent misplaced
cursors or focus.

* **Improvements**
* Caret normalization: clicks place the caret at the last meaningful
text position for consistent single-cursor behavior.

* **Tests**
  * Added end-to-end coverage for caret placement and focus transitions.
* New ratio-based click/double-click test utilities and a helper for
double-clicking note bodies.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/shared/src/__tests__/utils/range.unit.spec.ts

@@ -0,0 +1,108 @@
+import {
+  beforeEach,
+  describe,
+  expect,
+  it,
+  type MockInstance,
+  vi,
+} from 'vitest';
+
+import * as PointToRangeUtils from '../../utils/dom/point-to-range';
+import { handleNativeRangeAtPoint } from '../../utils/dom/point-to-range';
+
+describe('test handleNativeRangeAtPoint', () => {
+  let caretRangeFromPointSpy: MockInstance<
+    (clientX: number, clientY: number) => Range | null
+  >;
+  let resetNativeSelectionSpy: MockInstance<(range: Range | null) => void>;
+
+  beforeEach(() => {
+    caretRangeFromPointSpy = vi.spyOn(
+      PointToRangeUtils.api,
+      'caretRangeFromPoint'
+    );
+    resetNativeSelectionSpy = vi.spyOn(
+      PointToRangeUtils.api,
+      'resetNativeSelection'
+    );
+  });
+
+  it('does nothing if caretRangeFromPoint returns null', () => {
+    caretRangeFromPointSpy.mockReturnValue(null);
+
+    handleNativeRangeAtPoint(10, 10);
+    expect(resetNativeSelectionSpy).not.toHaveBeenCalled();
+  });
+
+  it('keeps range untouched if startContainer is a Text node', () => {
+    const div = document.createElement('div');
+    div.textContent = 'hello';
+
+    const text = div.firstChild!;
+
+    const range = document.createRange();
+    range.setStart(text, 2);
+    range.collapse(true);
+
+    caretRangeFromPointSpy.mockReturnValue(range);
+
+    handleNativeRangeAtPoint(10, 10);
+
+    expect(range.startContainer).toBe(text);
+    expect(range.startOffset).toBe(2);
+    expect(resetNativeSelectionSpy).toHaveBeenCalled();
+  });
+
+  it('moves caret into direct text child when clicking element', () => {
+    const div = document.createElement('div');
+    div.append('hello');
+
+    const range = document.createRange();
+    range.setStart(div, 1);
+    range.collapse(true);
+
+    caretRangeFromPointSpy.mockReturnValue(range);
+
+    handleNativeRangeAtPoint(10, 10);
+
+    expect(range.startContainer.nodeType).toBe(Node.TEXT_NODE);
+    expect(range.startContainer.textContent).toBe('hello');
+    expect(range.startOffset).toBe(5);
+    expect(resetNativeSelectionSpy).toHaveBeenCalled();
+  });
+
+  it('moves caret to last meaningful text inside nested element', () => {
+    const div = document.createElement('div');
+    div.innerHTML = `<span>a</span><span><em>b</em>c</span>`;
+
+    const range = document.createRange();
+    range.setStart(div, 2);
+    range.collapse(true);
+
+    caretRangeFromPointSpy.mockReturnValue(range);
+
+    handleNativeRangeAtPoint(10, 10);
+
+    expect(range.startContainer.nodeType).toBe(Node.TEXT_NODE);
+    expect(range.startContainer.textContent).toBe('c');
+    expect(range.startOffset).toBe(1);
+    expect(resetNativeSelectionSpy).toHaveBeenCalled();
+  });
+
+  it('falls back to searching startContainer when offset element has no text', () => {
+    const div = document.createElement('div');
+    div.innerHTML = `<span></span><span>ok</span>`;
+
+    const range = document.createRange();
+    range.setStart(div, 1);
+    range.collapse(true);
+
+    caretRangeFromPointSpy.mockReturnValue(range);
+
+    handleNativeRangeAtPoint(10, 10);
+
+    expect(range.startContainer.textContent).toBe('ok');
+    expect(range.startOffset).toBe(2);
+    expect(resetNativeSelectionSpy).toHaveBeenCalled();
+  });
+});