fix(calendar): preserve day column alignment when centering grid

lipgloss.PlaceHorizontal centers each line independently, which shifts
short last rows (e.g. "29 30" in Nov 2026) into wrong columns. Fix by
padding all grid lines to uniform width first via padLines(), then
indenting the whole block with a uniform left margin.

Added TestCalendarGridColumnAlignment to verify Nov 2026 day 29 (Sun)
and day 30 (Mon) align with their respective column headers.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: cpcloud

internal/app/calendar.go

@@ -84,27 +84,47 @@ func calendarGrid(cal calendarState, styles Styles) string {
 		hintStyle.Render("enter pick · esc cancel"),
 	)
 
-	// The grid is 20 chars wide ("Su Mo Tu We Th Fr Sa"); center everything
-	// to the wider of the grid and hints so the box looks balanced.
+	// The day-label row defines the grid's intrinsic width (20 visible cols).
+	// Pad every grid line to that width so the block is rectangular, then
+	// center the whole block within the wider hint line.
 	calW := lipgloss.Width(dayLabels)
+	gridBlock := padLines(grid.String(), calW)
+
 	hintW := lipgloss.Width(hints)
 	boxW := calW
 	if hintW > boxW {
 		boxW = hintW
 	}
 
-	center := func(s string) string {
+	// centerBlock centers a pre-padded rectangular block (all lines same
+	// width) by indenting every line uniformly. Unlike PlaceHorizontal this
+	// preserves internal column alignment.
+	centerBlock := func(s string, blockW int) string {
+		pad := (boxW - blockW) / 2
+		if pad <= 0 {
+			return s
+		}
+		indent := strings.Repeat(" ", pad)
+		lines := strings.Split(s, "\n")
+		for i, line := range lines {
+			lines[i] = indent + line
+		}
+		return strings.Join(lines, "\n")
+	}
+
+	// Single-line items can use PlaceHorizontal safely.
+	centerLine := func(s string) string {
 		return lipgloss.PlaceHorizontal(boxW, lipgloss.Center, s)
 	}
 
 	return lipgloss.JoinVertical(
 		lipgloss.Left,
-		center(header),
+		centerLine(header),
 		"",
-		center(dayLabels),
-		center(grid.String()),
+		centerBlock(dayLabels, calW),
+		centerBlock(gridBlock, calW),
 		"",
-		center(hints),
+		centerLine(hints),
 	)
 }
 
@@ -116,6 +136,19 @@ func sameDay(a, b time.Time) bool {
 	return a.Year() == b.Year() && a.Month() == b.Month() && a.Day() == b.Day()
 }
 
+// padLines right-pads each line in s so every line is exactly width visible
+// columns. This makes the block rectangular so uniform indentation preserves
+// internal column alignment.
+func padLines(s string, width int) string {
+	lines := strings.Split(s, "\n")
+	for i, line := range lines {
+		if w := lipgloss.Width(line); w < width {
+			lines[i] = line + strings.Repeat(" ", width-w)
+		}
+	}
+	return strings.Join(lines, "\n")
+}
+
 // calendarMove adjusts the calendar cursor by the given number of days.
 func calendarMove(cal *calendarState, days int) {
 	cal.Cursor = cal.Cursor.AddDate(0, 0, days)

internal/app/calendar_test.go

@@ -242,6 +242,62 @@ func TestCalendarYearNavigation(t *testing.T) {
 	}
 }
 
+func TestCalendarGridColumnAlignment(t *testing.T) {
+	// Nov 2026 starts on Sunday, so days 29 (Mon) and 30 (Tue) are on the
+	// last row. They must appear in the Mon and Tue columns, not shifted by
+	// centering logic.
+	styles := DefaultStyles()
+	cal := calendarState{
+		Cursor:   time.Date(2026, 11, 1, 0, 0, 0, 0, time.Local),
+		HasValue: false,
+	}
+	grid := calendarGrid(cal, styles)
+
+	// Find the day-label line and the last-row line.
+	lines := strings.Split(grid, "\n")
+	labelIdx := -1
+	lastDayIdx := -1
+	for i, line := range lines {
+		if strings.Contains(line, "Su Mo Tu We Th Fr Sa") {
+			labelIdx = i
+		}
+		if strings.Contains(line, "29") && strings.Contains(line, "30") {
+			lastDayIdx = i
+		}
+	}
+	if labelIdx < 0 {
+		t.Fatal("day-label line not found")
+	}
+	if lastDayIdx < 0 {
+		t.Fatal("line with 29 and 30 not found")
+	}
+
+	// Nov 1, 2026 is a Sunday, so day 29 = Sunday ("Su" column) and
+	// day 30 = Monday ("Mo" column). Verify both align correctly.
+	suPos := strings.Index(lines[labelIdx], "Su")
+	moPos := strings.Index(lines[labelIdx], "Mo")
+	pos29 := strings.Index(lines[lastDayIdx], "29")
+	pos30 := strings.Index(lines[lastDayIdx], "30")
+	if suPos < 0 || pos29 < 0 {
+		t.Fatalf("could not find Su (%d) or 29 (%d)", suPos, pos29)
+	}
+	if suPos != pos29 {
+		t.Errorf(
+			"column misalignment: Su at col %d but 29 at col %d\nlabels: %q\nlast:   %q",
+			suPos, pos29, lines[labelIdx], lines[lastDayIdx],
+		)
+	}
+	if moPos < 0 || pos30 < 0 {
+		t.Fatalf("could not find Mo (%d) or 30 (%d)", moPos, pos30)
+	}
+	if moPos != pos30 {
+		t.Errorf(
+			"column misalignment: Mo at col %d but 30 at col %d\nlabels: %q\nlast:   %q",
+			moPos, pos30, lines[labelIdx], lines[lastDayIdx],
+		)
+	}
+}
+
 func TestOpenCalendarWithEmptyValue(t *testing.T) {
 	m := newTestModel()
 	dateVal := ""