Say what a button without words does when the pointer rests (#209)

The top bar, the magnet, the eye and many marks of the inspector are
pictures without a caption. Whoever did not know one could only try
it. The toolkit had no hint on hover, which also forced the point
menu of #195 to be words. The answers in the issue settle the open
points: a cut tab name shows in full, shortcuts are part of the
text, the point menu stays as it is.

- Button takes a tooltip, a text or a function asked each time. It
  shows on a small sign once the pointer has rested for half a
  second.
- There is one sign for the page, a TooltipLayer on the overlay
  above the menus. A control reports each pointer move and the
  pointer leaving, the layer does the waiting.
- A press, a key, the wheel or a blur of the window takes the sign
  away. initUI listens for them on the window.
- placeTooltip in ui/tooltip.ts is the rule for the place as a pure
  function: under the control and flush left, flush right at the
  right border, above the control at the bottom.
- toolbarTip says what the five buttons of the top bar do right now.
  Undo and redo name their step from CommandStack.undoLabel and
  redoLabel, as in "Undo Paint tiles (Ctrl+Z)".
- A SortableList reports its own marks with a key per mark: the eye,
  the duplicate mark, the cross and the plus.
- The magnet, both fullscreen buttons, the eye of the scene tab, the
  overflow of the tab strip, the plus of the assets panel, the marks
  of the inspector rows and the nine anchors of the resize dialog
  carry a text.

Decided here:

- Every button whose text is cut short shows the whole text, not
  only a tab.
- A row action of the inspector names the one thing a click does. A
  button that opens a menu says only Reset, Apply or Size from the
  picture.
- A button just clicked stays quiet until the pointer has left it.
- A greyed out button shows no sign.
- The switches of the eye popup, the cross of a document tab and the
  tools of pixel art have none. The tools carry words, other than
  the issue assumes.
- The marks of a list say Show or Hide, Duplicate, Remove and Add,
  whatever the list holds.

Found on the way:

- Signing out empties the overlay and would have destroyed a sign on
  screen with it. The editor takes the tooltip away first. This has
  no test of its own.
- The text hooks locate and has skip the sign, or it would answer
  for the button under it.

Tests:
- Gate on melektaus-atx: 210 files, 3209 tests (3176 + 33), exit 0
- e2e 46 on melektaus-atx: 20 checks, all pass
- e2e 1-14 on melektaus-atx: 508 checks, all pass
- e2e 1-9,14,39,40,44-48: 685 pass, 2 fail, both in module 14. It
  measures tabs that modules 10 to 13 open, and the chain 1-14 is
  green. The cut chain was not run on the state before.
- No full run and no smokes. The sum of 1667 (1664 + 3) is reckoned,
  1664 is what CI counted for 3452899.
- 33 unit tests in tests/ui/tooltip.test.ts
- Three e2e checks in block 46h of module 46: the redo button after
  the wait, taking the sign away, turning at the right border
- 50 unit counter-probes and four browser counter-probes all fail
  their tests. Three of the unit ones did not at first and got
  sharper tests.
- Not checked in the browser: the sign of a cut tab, the marks of
  the lists, turning upwards at the bottom, each other button alone

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/graph/SnapToggle.ts

@@ -16,6 +16,7 @@ export class SnapToggle {
       width: Theme.controlHeight,
       icon: HEADER_ICON_SVG.snap,
       toggle: true,
+      tooltip: 'Snap to the grid',
       onClick: () => this.set(!this.on),
     });
   }