feat(tui): bordered modals, welcome state, and dynamic name width

- Delete confirmation wrapped in rounded border box with danger color
- Empty sites view shows styled welcome box with onboarding hint
- NAME column width scales with terminal width (13-40 chars)

internal/tui/tab_sites.go

@@ -195,11 +195,31 @@ func fmtStatus(status string, paused bool) string {
 	}
 }
 
+func (m Model) nameWidth() int {
+	w := m.termWidth - 105
+	if w < 13 {
+		w = 13
+	}
+	if w > 40 {
+		w = 40
+	}
+	return w
+}
+
 func (m Model) viewSitesTab() string {
 	const sparkWidth = 20
 
 	if len(m.sites) == 0 {
-		return "\n  No sites configured. Press [n] to add one."
+		welcome := lipgloss.NewStyle().
+			Border(lipgloss.RoundedBorder()).
+			BorderForeground(lipgloss.Color("#7D56F4")).
+			Padding(1, 3).
+			Render(
+				titleStyle.Render("Go-Upkeep") + "\n\n" +
+					"No monitors configured yet.\n\n" +
+					subtleStyle.Render("[n] Add your first monitor"),
+			)
+		return "\n" + welcome
 	}
 
 	colWidths := []int{6, 0, 10, 10, 8, 8, sparkWidth + 4, 7, 9}
@@ -222,7 +242,7 @@ func (m Model) viewSitesTab() string {
 					}
 					rows = append(rows, []string{
 						strconv.Itoa(i + 1),
-						m.zones.Mark(fmt.Sprintf("site-%d", i), arrow+" "+limitStr(site.Name, 11)),
+						m.zones.Mark(fmt.Sprintf("site-%d", i), arrow+" "+limitStr(site.Name, m.nameWidth()-2)),
 						"group",
 						fmtStatus(site.Status, site.Paused),
 						subtleStyle.Render("—"),
@@ -240,9 +260,9 @@ func (m Model) viewSitesTab() string {
 					if i+1 >= len(m.sites) || m.sites[i+1].ParentID != site.ParentID {
 						prefix = "└"
 					}
-					name = prefix + " " + limitStr(name, 11)
+					name = prefix + " " + limitStr(name, m.nameWidth()-2)
 				} else {
-					name = limitStr(name, 13)
+					name = limitStr(name, m.nameWidth())
 				}
 
 				hist, _ := m.engine.GetHistory(site.ID)