Show a wheel step or Fit as a short zoom transition (#309)

The wheel and the Fit button used to jump to the new view. Now the
view takes a short way there, 200 ms by default, everywhere the editor
zooms. The zoom steps stay the same, only the change is shown.

- viewTween: tweenView is the way between two views as a pure
  function. The scale moves by equal ratios, and the world point that
  sits at the same place on screen in both views stays there. After a
  wheel step that is the point under the pointer.
- ViewTween drives it on the ticker. A surface hands it reading,
  writing and drawing its own view and wraps its wheel and Fit code in
  change(). A step during a transition starts from where that one was
  heading, so quick steps add up to exactly as many steps.
- Anything else that moves the view ends the transition. A pan jumps
  to the target first, and saving a view saves the target.
- Wired into FreeViewport (Scene, Container, animation preview),
  SheetCanvas (Texture, Curve, Pixel art, Vector art), GraphCanvas,
  panAndZoom (Tile board, plugin node board) and the timeline.
- Menu > General settings... sets the time in ms, 0 jumps at once. It
  is kept in this browser like the panel sizes, not in the project,
  and it is not an undo step.
- A document that opens still comes up framed at once. The animation
  preview frames a new subject itself instead of calling fit().
- The pixel art readout names the step the view is heading for.

Measured in the scene view at 200 ms on melektaus-atx, where every
frame of the transition is a full redraw:

- 500 sprites: redraw 6.7 ms, 16 frames, mean 18 ms
- 1000 sprites: redraw 13.0 ms, 9 frames, mean 27 ms
- 2000 sprites: redraw 32.2 ms, 5 frames, mean 58 ms

Tests:
- The harness sets 0 ms on every load, so the existing modules read
  the step and not the way.
- e2e 46i samples one wheel step at 1000 ms a frame later: zoom 1.033
  between 1 and 2, the point under the pointer kept at (134, -40). It
  lands on the view a 0 ms jump reaches.
- e2e 46 and 49 expect the new menu entry.
- Gate (atx): 234 files, 3563 tests, CHECK EXIT 0 (+15)
- e2e 46,49 (atx): ALL PASSED, 43 checks (+3, sum 1735)
- Three counter-checks fail view-tween.test.ts as expected. e2e 46i
  fails when the scene view does not carry its centre along.

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

src/editor/Editor.ts

@@ -45,6 +45,8 @@ import type { ReleaseStore } from '../core/store/ReleaseStore';
 import type { ReleaseDialog } from './ReleaseDialog';
 import type { ProjectSettingsDialog } from './ProjectSettingsDialog';
 import { dialogSlot } from './FormDialog';
+import { generalSettings, keepGeneralSettings } from './generalSettings';
+import { GeneralSettingsDialog } from './GeneralSettingsDialog';
 import { ContainerEditor } from './container/ContainerEditor';
 import { EditorRun } from './EditorRun';
 import { GraphEditor } from './graph/GraphEditor';
@@ -256,6 +258,7 @@ export class Editor implements PlayHost {
   plugins: PluginManager | null = null;
   private readonly toolbar: Toolbar;
   private readonly passwordDialog = dialogSlot<PasswordDialog>();
+  private readonly generalDialog = dialogSlot<GeneralSettingsDialog>();
   /** Drawn-frame count at the last measurement, not a counter of its own. */
   private fpsFrames = 0;
   private fpsElapsed = 0;
@@ -601,11 +604,22 @@ export class Editor implements PlayHost {
     const open = () => this.openDocument('management');
     return [
       { separator: true },
+      { label: 'General settings…', onSelect: () => this.openGeneralSettings() },
       ...(this.usersPane ? [{ label: 'User management', onSelect: open }] : []),
       { label: 'Plugins', onSelect: open },
     ];
   }
 
+  /** What the editor does for whoever sits at it, kept in this browser (#309). */
+  openGeneralSettings(): GeneralSettingsDialog {
+    return this.generalDialog.open(new GeneralSettingsDialog(generalSettings(), keepGeneralSettings));
+  }
+
+  /** The open "General settings" dialog, for the check scripts. */
+  generalSettingsDialog(): GeneralSettingsDialog | null {
+    return this.generalDialog.current();
+  }
+
   /**
    * The account menu under its button (#182). The name stands in it as an entry that cannot be
    * picked: it says who is signed in without costing the crowded toolbar another label.
@@ -921,6 +935,7 @@ export class Editor implements PlayHost {
     for (const cleanup of this.cleanups.splice(0).reverse()) cleanup();
     // Closed rather than just thrown away with the overlay below, so the slot lets go of it too.
     this.passwordDialog.current()?.close();
+    this.generalDialog.current()?.close();
     // The tooltip is not the editor's to destroy: it leaves the overlay before that is emptied.
     tooltips.dismiss();
     // A menu or a picker left open belongs to widgets that are about to be destroyed.