Add drag erase, a laser, type-to-add, Tab and a command palette

[raj-khan]

FL-83, part 1 of 2 (frames follow in part 2).

• Eraser: click or drag across shapes and connections; everything it touched is marked, then deleted as one undoable change
• Laser (8/K): a glowing trail that follows the pointer and fades, for presenting; nothing is saved. Left off the phone tool bar, which only has room for seven 44px buttons
• Typing on a blank diagram starts a shape named with what is typed, ahead of the one-letter tool keys. Keys (and an early Enter) are buffered until the new title field has focus, because the shape is created asynchronously
• Double click on empty canvas adds a shape there, ready to name
• Tab adds the next step below the selected (or focused) shape, of the same kind, connected and ready to name, as in Whimsical; placed where nothing is, with its source pinned
• Ctrl+K opens a command palette over every menu action, tool, view action and shape (Add …), built from the same registries, so new shapes and tools appear without a line of their own; also in the menu and in help

Tests: e2e/quick.spec.js (6); unit tests for withConnectedShape, withErased, filterCommands. e2e 131, vitest 261, lint and typecheck.