feat(tui): add split-pane detail, compact date headers, and input drawer

Three layout improvements for better space utilization:

- Compact date headers: date labels render as left gutter column instead
  of standalone lines, saving one line per date group in stream view
- Input drawer: capture bar expands to 4-line drawer with border, hints,
  and live preview of parsed entity/search query
- Split-pane detail: wide terminals (>=100 cols) show list and detail
  side-by-side with h/l focus switching, falling back to full-screen
  detail on narrow terminals

internal/tui/help.go

@@ -50,6 +50,11 @@ func renderHelp(width, height int) string {
 			{"enter", "copy resolved"},
 			{"esc", "cancel"},
 		}},
+		{"Split View", [][2]string{
+			{"l", "focus detail pane"},
+			{"h", "focus list pane"},
+			{"esc", "close detail / back"},
+		}},
 		{"Global", [][2]string{
 			{"?", "toggle help"},
 			{"q / ctrl+c", "quit"},