feat(ribbon): collapse overflowing panels to flyout buttons, anchor dropdowns to their widget

Third stage of the adaptive tool area (shrink -> compact -> collapse).
When even the compact panels don't fit, DensitySwap picks a new
CollapsePanels widget that keeps a left prefix of panels inline and
collapses the rest to buttons; clicking a button opens the full panel as
an overlay flyout anchored below it (closes on outside press, mirroring
color_select's Floating).

A collapsed panel's button shows a live representative tool — the panel's
last-used tool (tracked per panel in Ribbon::note_panel_tool on every
tool click), defaulting to its first — rendered as a large icon. To
support this, render_small now also renders Large* items small and
render_large now renders plain Tool/Dropdown items large. Large dropdowns
render as icon + label + a bottom arrow strip via a shared
render_large_dropdown helper, used in both the full ribbon and collapsed
panels.

Ribbon dropdowns (tool dropdowns + undo/redo history) now anchor their
overlay directly below their widget at any size: a transparent PosReport
wrapper records each dropdown button's screen bounds into a thread-local
map on draw, and the overlays read it via Ribbon::dd_anchor instead of the
layout-estimating compute_*_left helpers.

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

src/app/update/mod.rs

@@ -1655,6 +1655,10 @@ impl OpenCADStudio {
                 self.ribbon.toggle_dropdown(&id);
                 Task::none()
             }
+            Message::ToggleRibbonPanel(id) => {
+                self.ribbon.toggle_collapsed_panel(&id);
+                Task::none()
+            }
             Message::CloseRibbonDropdown => {
                 self.ribbon.close_dropdown();
                 Task::none()