Moments across up to four pages: stacked in Flow, side by side in Page/Book (BL-0055)

The save sheet gets "+ Previous page" / "+ Next page" (right to left for
rtl in Page/Book) for a picture that runs over several pages. Moments
store a layout (row | column); pages the selected region does not touch
are dropped. Crops, viewer and gallery draw both layouts.

Dialogs now clean up directly instead of waiting for the "close" event,
which a backgrounded page can deliver late (a closed sheet stayed in the
page and M stopped working).

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

docs/architecture.md

@@ -152,8 +152,9 @@ This keeps ids human-readable and derivable without a database. The price: renam
   "notes":     { "admin": [ { "id": "a1b2c3d4e5f6", "t": 1790797300000, "m": "Moon Garden", "c": "2/6",
                               "text": "Moon Garden · Ch. 6: Frost", "read": false } ] },
   "moments":   { "admin": [ { "id": "9f1c2b3a4d5e", "m": "Moon Garden", "c": "1/2", "v": "c0002 Roots [MangaDex]",
-                              "i": [4], "f": ["0005.png"], "sha": ["<sha256 of the file>"],   // pages, left to right as displayed (1 or 2)
-                              "region": { "x": 0.1, "y": 0.5, "w": 0.5, "h": 0.25 },          // fractions of the page(s); null = whole page
+                              "i": [4], "f": ["0005.png"], "sha": ["<sha256 of the file>"],   // 1–4 pages in displayed order
+                              "layout": "row",                                                // "row" side by side (Page/Book), "column" stacked (Flow)
+                              "region": { "x": 0.1, "y": 0.5, "w": 0.5, "h": 0.25 },          // fractions of the pages put together; null = all
                               "cat": "awesome", "note": "", "t": 1790797400000 } ] },
   "votes":     { "Moon Garden": { "1/2": { "c0002 Roots [Official]": { "admin": 1, "reader": -1 } } } },
   "known":     { "Moon Garden": ["1/1", "1/2", "1/2.5", "..."] }   // every chapter id ever seen (append-only)
@@ -206,7 +207,7 @@ All requests and responses are JSON. POSTs require `Content-Type: application/js
 | `POST /api/vote` `{m, c, v, value: 1\|-1\|0}` | user | Vote a version; returns the re-ranked versions |
 | `POST /api/follow` `{m, on}` | user | Follow a manga for notifications |
 | `GET /api/moments?m=` | user | The caller's moments of that manga in story order: category, note, region, chapter, `order`, page images, `missing` when a page file is gone. `/api/chapter` also lists the caller's moments on the opened version |
-| `POST /api/moments` `{m, c, v, pages, region, cat, note}` | user | Save a moment: `pages` are 1–2 indexes left to right as displayed, `cat` one of `twist hot awesome cute funny feels` (required), `region` fractions or null |
+| `POST /api/moments` `{m, c, v, pages, layout, region, cat, note}` | user | Save a moment: `pages` are 1–4 distinct indexes in displayed order, `layout` `row` (default) or `column`, `cat` one of `twist hot awesome cute funny feels` (required), `region` fractions of the pages put together, or null |
 | `POST /api/moments/update` `{id, cat?, region?, note?}` · `POST /api/moments/delete` `{id}` | user | Edit or delete one of the caller's own moments (another user's id is `404`) |
 | `GET /api/notifications` · `POST /api/notifications/read` `{id \| all}` | user | Notification list and read state |
 | `GET /api/admin` | admin | Users, last scan result, library path |
@@ -359,7 +360,7 @@ mode       = adapt && intended ∉ compatible ? compatible[0] : intended
 - Pulses are sent at most every 10 seconds and on pause/page exit. The server validates the manga/chapter/version and page indices, de-duplicates `(session, seq)`, clamps time to server-observed intervals and stores compact page ranges separately from ordinary progress.
 - The bottom toolbar chip shows active time and the current state; its panel adds pass time, verified pages, predominant input and loading wait.
 
-**Moments** (`public/moments.js`): the top bar's bookmark button (or `m`) opens a sheet for the page(s) on screen: in Flow the page at the reading line, in Book the spread. A rectangle dragged over the preview keeps only that region; a region inside one page of a spread saves that page alone. Exactly one category is required. The button is filled when the page already has a moment. The manga page shows the user's moments as a strip of crops (sort by story or by date saved, category filters from five moments), with a viewer to step through them, edit, delete or open the reader at `read.html?…&p=<page index>`. Crops position the full page images inside a clipping box; nothing is generated on the server.
+**Moments** (`public/moments.js`): the top bar's bookmark button (or `m`) opens a sheet for the page(s) on screen: in Flow the page at the reading line, in Book the spread. "+ Previous page" / "+ Next page" add neighbours (up to four pages) for a picture that runs over several pages: stacked in Flow (`column`), side by side in Page and Book (`row`, right to left for `rtl`). A rectangle dragged over the preview keeps only that region, and pages it does not touch are left out. Exactly one category is required. The button is filled when the page already has a moment. The manga page shows the user's moments as a strip of crops (sort by story or by date saved, category filters from five moments), with a viewer to step through them, edit, delete or open the reader at `read.html?…&p=<page index>`. Crops position the full page images inside a clipping box; nothing is generated on the server.
 
 **Zoom persistence:** per mode key (`flow`, `page`, `book`, `strip`), saved 800 ms after the last change.