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>

frontend/src/features/notes/NoteEditor.jsx

@@ -435,6 +435,16 @@ export function NoteEditor({
         display: "flex",
         flexDirection: "column",
         height: "100%",
+        /* Fill the pane rather than the toolbar.
+         *
+         * As a flex item with the default `flex: 0 1 auto` this box was as wide
+         * as its widest row — the toolbar. Switching to Draw swaps a dozen
+         * formatting buttons for six drawing ones, the toolbar's natural width
+         * collapses, and the page took it with it: the paper measurably shrank
+         * from 733px to 460px on the same screen. Growing to the pane makes the
+         * width a property of the window, which is what it always looked like. */
+        flex: 1,
+        minWidth: 0,
         background: isMobileViewport
           ? T.bg
           : dark
@@ -464,6 +474,7 @@ export function NoteEditor({
             T={{ ...T, danger: "#e5534b" }}
             icons={I}
             compact={isMobileViewport}
+            dark={dark}
           />
         ) : (
           <>