feat(ui): elide overflowing text, tooltip full layer name

iced has no built-in ellipsis, so long user content (file names, layer
names, paths, property values) wrapped or spilled past fixed-width
panels. Add an `elide` helper (char-budget truncation with a trailing
ellipsis) and apply it to the layer manager, properties panel, document
tabs, recent-files list and the save dialog.

In the layer manager a truncated name reveals its full text in a
cursor-following tooltip on hover, so the column need not be widened.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/mod.rs

@@ -27,6 +27,7 @@ pub mod statusbar;
 pub mod statusbar_config;
 pub mod statusbar_menu;
 pub mod tablestyle;
+pub mod text_util;
 pub mod textstyle;
 pub mod units_popup;