feat(tui): lazygit-style titled panel borders

All panels wrapped in titled rounded borders (╭─ Title ──╮). Focused
panel gets accent-colored border, unfocused panels get muted border.

- Monitors panel: titled "Monitors", focused when detail is closed
- Logs panel: titled "Logs", always unfocused (passive display)
- Detail panel: titled with monitor name, focused when open

Table's own RoundedBorder replaced with HiddenBorder — the titled
panel border provides the visual frame, table uses space-separated
columns internally. Consistent chrome across all panels.

internal/tui/table_helpers.go

@@ -52,8 +52,7 @@ func (m Model) renderTable(headers []string, items int, buildRows func(start, en
 	}
 
 	t := table.New().
-		Border(lipgloss.RoundedBorder()).
-		BorderStyle(m.st.tableBorderStyle).
+		Border(lipgloss.HiddenBorder()).
 		Width(tableWidth).
 		Headers(headers...).
 		Rows(rows...).
@@ -94,5 +93,5 @@ func (m Model) renderTable(headers []string, items int, buildRows func(start, en
 			return base
 		})
 
-	return "\n" + t.Render()
+	return t.Render()
 }