chore(tui): delete dead braille code, hoist sparkWidth, stop resize flash

1. Delete braille.go + braille_test.go — dead code, only referenced
   by its own test. Can be re-added when latency charts are built.

2. Hoist duplicate `const sparkWidth = 40` (update.go + view_detail.go)
   to package-level `detailSparkWidth`. Click-index resolution and
   rendering now share one constant.

3. Remove tea.ClearScreen on every resize — caused full-screen flash
   during continuous resizes. ctrl+l manual clear kept.

internal/tui/view_detail.go

@@ -207,9 +207,8 @@ func (m Model) viewDetailPanel() string {
 	}
 
 	b.WriteString(m.divider() + "\n")
-	const sparkWidth = 40
 	if site.Type == "push" {
-		b.WriteString("  " + m.zones.Mark("spark-heartbeat", m.heartbeatSparkline(hist.Statuses, sparkWidth, "")))
+		b.WriteString("  " + m.zones.Mark("spark-heartbeat", m.heartbeatSparkline(hist.Statuses, detailSparkWidth, "")))
 		if len(hist.Statuses) > 0 {
 			up := 0
 			for _, s := range hist.Statuses {
@@ -222,7 +221,7 @@ func (m Model) viewDetailPanel() string {
 				up, len(hist.Statuses))
 		}
 	} else {
-		b.WriteString("  " + m.zones.Mark("spark-latency", m.latencySparkline(hist.Latencies, hist.Statuses, sparkWidth, "")))
+		b.WriteString("  " + m.zones.Mark("spark-latency", m.latencySparkline(hist.Latencies, hist.Statuses, detailSparkWidth, "")))
 		var minL, maxL, total time.Duration
 		count := 0
 		for i, l := range hist.Latencies {
@@ -249,7 +248,7 @@ func (m Model) viewDetailPanel() string {
 	}
 
 	if m.sparkTooltipIdx >= 0 {
-		b.WriteString("\n" + m.renderSparkTooltip(site, hist, sparkWidth))
+		b.WriteString("\n" + m.renderSparkTooltip(site, hist, detailSparkWidth))
 	}
 
 	b.WriteString("\n")