Part of #394: Auto-Collapse Iconic Panels

[wstock]

Part of #394. Preferences › User Interface › Auto-Collapse Iconic Panels (autoCollapseIconPanels) was stored and never read: a panel popped out of the icon column stayed open until its » or its icon.

Now

• On: a press away from the flyout puts it away (a click on the canvas, a toolbar, a menu…), as in Illustrator.
• A press on the icon column is left to the icons, which swap or close the flyout themselves on release — acting on the press would have closed the flyout and then reopened it on the same icon's release.
• A press in a popup the flyout opened (its panel menu, a dropdown), which lies outside the flyout's rect, keeps it (egui::Popup::is_any_open).
• Off (the default, Illustrator's too): unchanged.

Tests

• dock::tests::auto_collapse_puts_a_flyout_away_on_a_click_elsewhere (the dock harness, headless egui frames on a 1600 × 1000 window): off, a click elsewhere leaves the Layers flyout; prefs.set autoCollapseIconPanels=true → a click elsewhere puts it away; its icon still pops it out; a click inside keeps it; another icon swaps it; the same icon puts it away.
• cargo test -p vectorcraft-ui-egui dock::tests 6/6; cargo clippy -p vectorcraft-ui-egui --all-targets -- -D warnings clean for the changed files (the only errors on main are the pre-existing chunks_exact ones in ui-egui/src/cursors.rs, allowed for the run). cargo fmt applied.

Docs

• ROADMAP: "Shipped so far", the parity row (38 → 37 options still unread) and the Last-updated line.
• docs/mcp.md: autoCollapseIconPanels added to the view preferences paragraph.

No new tl! literals (no catalog changes). Note: #484 and #486 (also #394, from me) each also take the ROADMAP count 38 → 37 on the same lines, so whichever lands last will need a one-word rebase.

Developed with AI assistance (Claude Code); reviewed and tested locally.

[bflatastic]

Thanks @wstock, sparing the icon column and the panel's own popups was well thought through. We added one commit:

• A click inside a dialog the panel opened (or on a dialog's backdrop) was putting the panel away underneath it. "Away" now means a press on no foreground layer and not on the modal backdrop, the same test the popovers use.
• A click in the expanded dock's panel group now puts the flyout away too, as a click anywhere else in the workspace does in Illustrator; only the icon column is spared. Your test covers both cases now.

Full cargo xtask ci passed on the integrated stack.