fix: center bullets and checkboxes in the marker column

Tests/ConjureKitTests/NotesEditingTests.swift

@@ -1250,17 +1250,48 @@ func renderedListMarkersPaintBulletsAndNumbersInsideTheirGlyphFrames() throws {
         context.cgContext.clear(CGRect(x: 0, y: 0, width: 160, height: 48))
         layout.drawGlyphs(forGlyphRange: glyphs, at: NSPoint(x: 4 - frame.minX, y: 10 - frame.minY))
         NSGraphicsContext.restoreGraphicsState()
-        var painted = false
+        var minX = 160, maxX = -1
         for y in 0..<48 {
             for x in 0..<160 where (bitmap.colorAt(x: x, y: y)?.alphaComponent ?? 0) > 0.1 {
-                painted = true
+                minX = min(minX, x)
+                maxX = max(maxX, x)
             }
         }
-        #expect(painted, "The actual TextKit draw path must paint the marker for \(source)")
+        #expect(maxX >= minX, "The actual TextKit draw path must paint the marker for \(source)")
+        if ["-", "*", "+"].contains(String(source.prefix(1))) {
+            #expect(abs(CGFloat(minX + maxX + 1) / 2 - (4 + frame.width / 2)) <= 1)
+        } else {
+            #expect(abs(CGFloat(maxX + 1) - frame.width) <= 3)
+        }
         #expect(editor.markdownString == source)
     }
 }
 
+@Test @MainActor
+func listCheckboxesStayCenteredInTheSharedColumnAtEachIndentation() throws {
+    _ = NSApplication.shared
+    let editor = NotesTextView(frame: NSRect(x: 0, y: 0, width: 400, height: 300))
+    let source = "- bullet\n- [ ] task\n12345. wide number\n  + nested bullet\n  - [x] nested task"
+    editor.setMarkdownContents(NSAttributedString(string: source))
+    let layout = try #require(editor.layoutManager)
+    let container = try #require(editor.textContainer)
+    layout.ensureLayout(for: container)
+    editor.layout()
+    let text = editor.string as NSString
+    let checkboxes = editor.subviews.compactMap { $0 as? NSButton }
+    for (index, label) in ["task", "nested task"].enumerated() {
+        let body = text.range(of: label)
+        let line = text.lineRange(for: body)
+        let marker = text.range(of: "\u{fffc}", options: [], range: line)
+        let glyphs = layout.glyphRange(forCharacterRange: marker, actualCharacterRange: nil)
+        let frame = layout.boundingRect(forGlyphRange: glyphs, in: container)
+            .offsetBy(dx: editor.textContainerOrigin.x, dy: editor.textContainerOrigin.y)
+        let checkbox = try #require(checkboxes.indices.contains(index) ? checkboxes[index] : nil)
+        #expect(abs(checkbox.frame.midX - frame.midX) <= 0.5)
+    }
+    #expect(editor.markdownString == source)
+}
+
 @Test @MainActor
 func listBodyInsertionUsesVisiblePositionForTypingPasteAndReplacementRanges() throws {
     _ = NSApplication.shared