refactor(tui): remove full-page detail, SLA, and history views

All monitor detail content now lives in the sidebar panel.
Delete the full-page viewDetailPanel, viewSLAPanel, viewHistoryPanel,
handleDetailKey, handleSLAKey, handleHistoryKey, openSLAView, and
related dead code (histogram, sparkline tooltip, detailViewport).

Remove stateDetail, stateSLA, stateHistory session states.
Update tests to use detailOpen/detailMode instead of removed states.

internal/tui/histogram.go

@@ -1,89 +0,0 @@
-package tui
-
-import (
-	"fmt"
-	"strings"
-	"time"
-
-	"github.com/charmbracelet/lipgloss"
-)
-
-type latencyBucket struct {
-	label string
-	min   int64
-	max   int64
-	count int
-}
-
-func (m Model) latencyHistogram(latencies []time.Duration, statuses []bool, width int) string {
-	if len(latencies) == 0 || width < 30 {
-		return ""
-	}
-
-	buckets := []latencyBucket{
-		{"0-50ms", 0, 50, 0},
-		{"50-100ms", 50, 100, 0},
-		{"100-200ms", 100, 200, 0},
-		{"200-500ms", 200, 500, 0},
-		{"500ms+", 500, 999999, 0},
-	}
-
-	for i, l := range latencies {
-		if i < len(statuses) && !statuses[i] {
-			continue
-		}
-		ms := l.Milliseconds()
-		for j := range buckets {
-			if ms >= buckets[j].min && ms < buckets[j].max {
-				buckets[j].count++
-				break
-			}
-		}
-	}
-
-	maxCount := 0
-	for _, b := range buckets {
-		if b.count > maxCount {
-			maxCount = b.count
-		}
-	}
-	if maxCount == 0 {
-		return ""
-	}
-
-	labelW := 10
-	countW := len(fmt.Sprintf("%d", maxCount))
-	barW := width - labelW - countW - 4
-	if barW < 5 {
-		barW = 5
-	}
-
-	var sb strings.Builder
-	for _, b := range buckets {
-		fill := 0
-		if maxCount > 0 {
-			fill = b.count * barW / maxCount
-		}
-
-		var barColor lipgloss.Style
-		switch {
-		case b.min < 100:
-			barColor = m.st.specialStyle
-		case b.min < 500:
-			barColor = m.st.warnStyle
-		default:
-			barColor = m.st.dangerStyle
-		}
-
-		bar := barColor.Render(strings.Repeat("█", fill))
-		if fill < barW {
-			bar += m.st.subtleStyle.Render(strings.Repeat("░", barW-fill))
-		}
-
-		label := fmt.Sprintf("%*s", labelW, b.label)
-		count := fmt.Sprintf("%*d", countW, b.count)
-		sb.WriteString("  " + m.st.subtleStyle.Render(label) + " " + bar + " " + count + "\n")
-	}
-
-	return sb.String()
-}