refactor(ui): app-wide compact, translucent tooltips

Add material::Tooltip / BeginTooltip / EndTooltip wrappers (tooltip_style.h)
that scope a small window padding (8x4, dpi-scaled) and ~85% opacity to
tooltips only, then route the tooltip call sites through them. Menus and combo
dropdowns are untouched (they keep the global opaque PopupBg).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/ui/material/draw_helpers.h

@@ -6,6 +6,7 @@
 
 #include "colors.h"
 #include "type.h"
+#include "tooltip_style.h"
 #include "../layout.h"
 #include "../schema/element_styles.h"
 #include "../schema/color_var_resolver.h"