[MarcelP102]

Summary

Makes docked and floating pallets steadier (the title bar keeps its side, every edge resizes, and the drawing no longer jumps), and makes the Blocks palette fast with many blocks.

Floating pallets (src/ui/dock.rs, src/app/dock)

• The vertical title bar keeps its side, saved with the layout. A layout saved before this change starts with the bar on the left.
  • It starts on the side the pallet was docked on.
  • While dragging, it only flips when the frame touches the docked pallets of an edge, the screen edge, or an edge showing the blue drop preview.
  • With docking off for the pallet, only the screen edge counts.
• The corner resize grip and its resize_left.svg icon are gone.
  • Every side and corner of a floating pallet resizes it, with the matching cursor.
  • Dragging the left or top side keeps the opposite side in place.
  • A pallet collapsed to its title bar resizes from the top and bottom only.
• Dragging a pallet that already floats moves the pallet itself, drawn where it will land. A layer above it takes the pointer, so the moving window doesn't react.
• A pallet dragged out of a dock still shows the plain drop ghost.

Drawing stays in place (dock_keep_view)

• Docking or undocking a pallet, switching an edge to auto-hide and resizing a docked group all keep the drawing where it is: the view pans by however far the viewport's centre moved.
• A revealed auto-hide group draws over the drawing instead of squeezing it.
• The viewport's new size is set as soon as the docked edges or the window change. The ViewCube's controls, the UCS picker and icon, the grid and the crosshair no longer trail the drawing by a frame while resizing.
• Split model viewports are not panned.

Blocks palette (src/ui/window/block_palette.rs, src/app/update/blocks_palette.rs)

• Thumbnails draw through a canvas cache, so they aren't tessellated again every frame.
• Block names are looked up through an index instead of a scan per card.
• Clicking a block that's already in the drawing no longer rebuilds every preview first. This removes about a second before the card turned blue.
• All six views build only the rows in view, with spaces of the same height for the rest:
  • names in Small Icons, Details and List stay on one line, cut with "…";
  • every row is the same height, which makes this possible;
  • List rows are about 1.7 px taller, as tall as Details rows.
• Previews are worked out once the palette is about to show them. The ribbon gallery, which shows every block, works them all out when it opens.
• Saving or defining a block (Block Editor save, Save As, BLOCK, block properties) redraws only that block and the blocks holding it. Every other change still rebuilds all previews.
• Library folders list at once, and their thumbnails, as well as those of Recent / Favorites drawings, are read on a background thread.

Testing

• cargo test --lib: 3,013 passed, 0 failed, 31 ignored, with upstream main merged in.
• New tests:
  • the title bar side: docked side, docked pallets, screen edge, drop preview, docking off;
  • resizing from every edge and the cursors;
  • the drawing keeping its place, and the viewport size following dock and window changes;
  • the moving window in the real view;
  • the palette's visible rows in every view, against the real iced layout;
  • on-demand previews, partial refreshes after a block save, the case-insensitive index and background thumbnails.
• cargo clippy --lib --tests shows no warnings in the new code.
• Measured with 500 blocks in a 300×1000 px palette (debug build), per frame:
  • name lookups: 21 ms → 1 ms;
  • drawing the visible thumbnails: 8 ms → 0.1 ms;
  • building and laying out the list: 9 ms → 0.7 ms.