Artboards panel: clicking an artboard makes it the active one

[theironchef]

Fixes #349.

Problem: the Artboards panel kept its own selection (pstate "ab-sel") that nothing outside the panel read. A click on a row highlighted it but didn't make that artboard active, so the status bar navigator, View › Fit Artboard in Window and Actual Size stayed on the previous artboard. The selection was also shared by every open document. In Illustrator, selecting an artboard's name in the panel makes it the active artboard (Select artboards).

Change (crates/ui-egui/src/panels/artboards.rs)

• The panel's selection is now the document view's active artboard, View::artboard, which the navigator and the Fit/Actual Size commands already use.
  • A row click sets it (the view doesn't move), as do the options icon, Move Up/Down and New Artboard.
  • The highlighted row follows the navigator.
  • It's per document.
• The panel menu's Duplicate and Delete Artboards act on that artboard.
• The panel's private ab-sel state is gone.

Tests

• New panels::artboards::tests::clicking_a_row_makes_its_artboard_active, with two artboards and headless frames with pointer events:
  • a click on "Artboard 2" makes the view's active artboard 1;
  • after the navigator's Previous, the panel's selection is 0 again.
• With the click not setting the view's artboard, the test fails.
• cargo test -p vectorcraft-ui-egui: 570 passed.
• cargo clippy -p vectorcraft-ui-egui --all-targets -- -D warnings (Rust 1.99): clean.
• cargo fmt --all -- --check: clean.
• Checked by hand in a release build on Windows with real mouse and keyboard input, with two artboards:
  • clicking "Artboard 2" in the Artboards panel set the view's active artboard to 1, and the status bar navigator read 2;
  • Ctrl+0 then fitted Artboard 2 (centre 500, 375; before the change it fitted Artboard 1);
  • the navigator's Previous moved the panel's highlight back to Artboard 1.

I didn't run the full cargo xtask ci (wasm step) here. The Artboard tool still keeps its own active artboard: making it follow the panel would be a separate change.

🤖 Generated with Claude Code

[bflatastic]

Thanks @theironchef, merged! A row click now makes that artboard the active one for the navigator and the Fit/Actual Size commands. I rebased it on main and added one commit on top:

• Double-clicking an artboard's number goes to it and fits it in the window, as in Illustrator; double-clicking the name still renames it.
• The Options button selects the Artboard tool on that row's artboard. With the Artboard tool, a click in the panel or on the canvas moves the tool's artboard, and the panel, the navigator and the tool now share one active artboard.
• A test and a ROADMAP line.

Live check: clicking Artboard 2 made it active with the view unchanged, double-clicking its number fitted it (navigator showed 2), and clicks with the tool on the canvas moved the panel's highlight.