Sort a notebook, import Markdown back, and stop the page shrinking in Draw

The paper measurably shrank on switching to Draw — 733px to 460px on the same
screen. The editor was a flex item at its default `flex: 0 1 auto`, so its width
was its widest row's: the toolbar. Swapping a dozen formatting buttons for six
drawing ones collapsed it. It now fills the pane, so the width is a property of
the window.

Each notebook remembers how its notes are ordered, on the server rather than per
device. The manual order has to survive being looked away from, so `reindex`
renumbers every note in the notebook rather than the filtered view, and dragging
is switched off while a search narrows the list. Reordering has its own route:
`PUT /notes/:id` would bump `updated_at` and snapshot a version, so a drag would
move a note to the top of "last changed" and spend a slot of its history.

Markdown and our own ZIP archives come back as notes, with their images
re-uploaded as attachments. A drawing returns as the PNG it was exported as —
vectors are not recoverable from pixels — and the import says so rather than
leaving it to be discovered. Writing the parser turned up a real bug in the
exporter: blocks were emitted with no blank line between them, so a list after a
list became one list and a quote after an item was read as part of it.

Creating or importing from "All Notes" now asks which notebook instead of
silently taking the first one. The web-link prompt is a real dialog: a bare
domain becomes https, javascript: is refused with a reason. The PDF viewer's
hide-drawing control is a labelled button rather than a filled-or-hollow dot,
and the export icon points down into a tray like every other download.

186 unit tests, 179 browser checks across eleven suites, including a new
`offline` suite that loads the app cold with the network off.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

e2e/export.mjs

@@ -100,7 +100,7 @@ try {
 
   /* ── single note as Markdown ── */
   await openExportDialog(p);
-  await p.getByRole("button", { name: /Markdown/ }).click();
+  await p.locator("[data-export-dialog]").getByRole("button", { name: /Markdown/ }).click();
   await p.waitForSelector("[data-export-done]", { timeout: 30000 });
   await p.waitForTimeout(600);
 
@@ -139,7 +139,7 @@ try {
 
   await clearDownloads(p);
   await openExportDialog(p);
-  await p.getByRole("button", { name: /Markdown/ }).click();
+  await p.locator("[data-export-dialog]").getByRole("button", { name: /Markdown/ }).click();
   await p.waitForSelector("[data-export-done]", { timeout: 30000 });
   await p.waitForTimeout(800);
   files = await downloads(p);
@@ -184,7 +184,7 @@ try {
   await p.waitForTimeout(500);
   check((await p.getByRole("button", { name: /PNG-Bild/ }).count()) > 0, "PNG is offered for the drawing");
   check(
-    (await p.getByRole("button", { name: /Markdown/ }).count()) === 0,
+    (await p.locator("[data-export-dialog]").getByRole("button", { name: /Markdown/ }).count()) === 0,
     "Markdown is not offered for a drawing, since it cannot hold one"
   );
   await p.getByRole("button", { name: /PNG-Bild/ }).click();
@@ -208,7 +208,7 @@ try {
   await p.getByRole("button", { name: /Nur den Notiztext/ }).click();
   await p.waitForTimeout(500);
   await clearDownloads(p);
-  await p.getByRole("button", { name: /Markdown/ }).click();
+  await p.locator("[data-export-dialog]").getByRole("button", { name: /Markdown/ }).click();
   await p.waitForSelector("[data-export-done]", { timeout: 30000 });
   await p.waitForTimeout(800);
   files = await downloads(p);