feat: F5.6d a drag is one change of the document; the others see it through the presence

Moving a device, moving or resizing a documentation item went into the
shared document at every pointer move: 59 updates a second, each leaving
about 18 bytes of history (M4 on test-filius). Now the editor keeps the drag
while it lasts, shows it itself and tells the others through the awareness
(moving, at most every 50 ms, the end at once), and writes it once when it
is let go. A drag the browser cancels or a second finger turns into a pinch
is written where it is; WebKit sends a second pointerdown for the first
finger when another comes, which had lost the drag.

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

packages/editor/browser/editorPage.ts

@@ -35,6 +35,11 @@ export function drawing(page: Page): Promise<TopologyView> {
   return page.evaluate(() => (window as unknown as { filiusDev: { view: () => TopologyView } }).filiusDev.view());
 }
 
+/** How many changes the document has had since the page opened it. */
+export function documentUpdates(page: Page): Promise<number> {
+  return page.evaluate(() => (window as unknown as { filiusDev: { updates: () => number } }).filiusDev.updates());
+}
+
 /** What the device sheet reads of a device. */
 export function sheetOf(page: Page, id: string): Promise<DeviceSheet | undefined> {
   return page.evaluate((each) => (window as unknown as { filiusDev: { sheet: (id: string) => DeviceSheet | undefined } }).filiusDev.sheet(each), id);