Type: font menu previews end safely, rows and samples cost less per frame (review of #339)

- A preview whose menu has gone (the panel isn't drawn: text deselected,
  panel closed) or is closing (Escape, a press outside the menu) is undone
  at the start of the frame, before the canvas sees the input: a canvas
  drag no longer runs inside the preview's interaction and gets rolled
  back with it. The menu also ends the preview in the frame it closes.
- The list fits the popup (it was taller than the popup, which then
  scrolled too), so the current family is centred in view on opening;
  ↑/↓ scroll only as far as needed.
- Type › Font (in-window menu bar): each item keeps room for its sample
  after the name, so long family names no longer run under it.
- Rows are listed again only when the query, filters, expanded families,
  favourites or font list change, not every frame.
- Samples: one budget per frame across every menu (Type › Font gave each
  item its own), at most 8 rendering at once, the worker asks for a
  repaint when it is done instead of polling, the cache holds 512, and
  one function draws a sample for both menus.
- Font menus use menu_family_list (the hidden-family rule lives there);
  FontClass::label is gone (the menu's translated labels are the only
  ones).
- Tests: a preview left by a menu that is gone is undone; a press
  outside the open menu ends the preview in that frame.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/text/src/fontdb.rs

@@ -379,20 +379,9 @@ pub enum FontClass {
 }
 
 impl FontClass {
+    /// The kinds a font menu filters by (all but `Other`).
     pub const ALL: [FontClass; 6] =
         [FontClass::Serif, FontClass::Sans, FontClass::Rounded, FontClass::Script, FontClass::Monospaced, FontClass::Decorative];
-
-    pub fn label(self) -> &'static str {
-        match self {
-            FontClass::Serif => "Serif / Mincho",
-            FontClass::Sans => "Sans Serif / Gothic",
-            FontClass::Rounded => "Rounded",
-            FontClass::Script => "Script / Brush",
-            FontClass::Monospaced => "Monospaced",
-            FontClass::Decorative => "Decorative",
-            FontClass::Other => "Other",
-        }
-    }
 }
 
 /// What a font menu filters on: whether a family sets Japanese, and its kind.