fix(tui): use panel width for table layout in split-pane mode

Table columns were computed from terminal width, causing row wrapping
when the monitors panel only gets 70% of the space. Introduced
contentWidth field set per-tab in viewDashboard. computeLayout,
isWide, and renderTable now use contentWidth for column visibility,
available space, and max table width calculations.

Columns gracefully hide (SSL, RETRIES, TYPE, UPTIME) when the panel
is narrower, matching the existing responsive breakpoint behavior.

internal/tui/tui.go

@@ -123,6 +123,7 @@ type Model struct {
 	maxTableRows    int
 	termWidth       int
 	termHeight      int
+	contentWidth    int
 	editID          int
 	editToken       string