fix(tui): correct table border overhead calculation

Was hardcoded to 30 — actual overhead is 2 (borders) + numCols-1
(separators) = 10 for 9 columns. The 20-char gap was being
redistributed by lipgloss into columns like # making them too wide.

internal/tui/tab_sites.go

@@ -360,8 +360,9 @@ func (m Model) computeLayout() tableLayout {
 		{"RT", "RETRIES", 5, 9},
 	}
 
-	overhead := 30
-	usable := m.termWidth - chromePadH - 2 - overhead
+	numCols := len(cols)
+	borderOverhead := 2 + (numCols - 1) // left + right border + column separators
+	usable := m.termWidth - chromePadH - 2 - borderOverhead
 	if usable < 80 {
 		usable = 80
 	}