feat(office): mail preview, infinite scroll, pane resize, and scrollbars

Polish the office TUI with proportional pane layout, drag resize, live
filtering, HTML mail preview, paginated mail lists, overflow scrollbars,
flattened navigation, and project save/status fixes; add UpdateProjectStatus.

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

cmd/office/ui/scrollbar.go

@@ -0,0 +1,76 @@
+package ui
+
+import (
+	"strings"
+
+	"github.com/charmbracelet/lipgloss"
+	"github.com/mattn/go-runewidth"
+)
+
+// ScrollbarMetrics computes thumb position for a vertical scrollbar.
+func ScrollbarMetrics(totalLines, viewportHeight, yOffset int) (show bool, thumbStart, thumbEnd int) {
+	if totalLines <= viewportHeight || viewportHeight < 1 {
+		return false, 0, 0
+	}
+	maxOff := totalLines - viewportHeight
+	if maxOff < 0 {
+		maxOff = 0
+	}
+	thumbSize := viewportHeight * viewportHeight / totalLines
+	if thumbSize < 1 {
+		thumbSize = 1
+	}
+	if thumbSize > viewportHeight {
+		thumbSize = viewportHeight
+	}
+	travel := viewportHeight - thumbSize
+	thumbStart = 0
+	if maxOff > 0 {
+		thumbStart = yOffset * travel / maxOff
+	}
+	return true, thumbStart, thumbStart + thumbSize
+}
+
+// ApplyVerticalScrollbar draws a 1-column scrollbar on the right when content overflows.
+func ApplyVerticalScrollbar(view string, width, height, totalLines, yOffset int) string {
+	show, thumbStart, thumbEnd := ScrollbarMetrics(totalLines, height, yOffset)
+	if !show || width < 2 {
+		return view
+	}
+	contentWidth := width - 1
+	lines := strings.Split(view, "\n")
+	for len(lines) < height {
+		lines = append(lines, "")
+	}
+	if len(lines) > height {
+		lines = lines[:height]
+	}
+	track := lipgloss.NewStyle().Foreground(lipgloss.Color("238"))
+	thumb := lipgloss.NewStyle().Foreground(lipgloss.Color("245"))
+	out := make([]string, height)
+	for row := 0; row < height; row++ {
+		line := padDisplayWidth(lines[row], contentWidth)
+		ch := "│"
+		style := track
+		if row >= thumbStart && row < thumbEnd {
+			ch = "█"
+			style = thumb
+		}
+		out[row] = line + style.Render(ch)
+	}
+	return strings.Join(out, "\n")
+}
+
+func padDisplayWidth(line string, width int) string {
+	if width < 1 {
+		return ""
+	}
+	w := runewidth.StringWidth(line)
+	if w > width {
+		return runewidth.Truncate(line, width, "")
+	}
+	if w < width {
+		line += strings.Repeat(" ", width-w)
+	}
+	return line
+}