Archive the whole data volume in Backups, not just the database

Settings > Backups gains a whole-data archive beside the database
snapshots, and both lists now fully work from the page.

- Data archives: `write-data-backup-archive.ts` tars all of DATA_DIR into
  BACKUP_ARCHIVE_DIR as cobble-data-<epoch-ms>.tar.gz, every entry under one
  root folder named after the archive, writing a .part name and renaming on
  success so a cut-off run is never listed. The newest
  AppData.DataBackupsKept are kept; db/.backups is left as it is.
- Restore: `restore-data-backup.ts` extracts to a temp dir, requires one
  root folder holding a db folder, takes a safety archive first, then
  replaces DATA_DIR (the database snapshots included) and `restart-app.ts`
  restarts the process through the docker socket, since the open SQLite
  handle points at the replaced file.
- Upload and restore: a modal over each list (database file or data
  archive), replacing the old /admin/settings/backups/restore page.
- Delete for both kinds, icon-only row actions shared through
  RowIconButton, and restore on every row.
- One backup or restore of either kind at a time (with-backup-run-lock).
- BACKUP_ARCHIVE_DIR is a start-up path (ProcessOnlyEnvKeys); the installer
  mounts $COBBLE_HOME/backups-archives at /backups-archives and recreates a
  container that lacks it. The image installs tar and gzip.

README.md

@@ -195,6 +195,7 @@ Everything that must survive an update lives under the install directory:
   .env                  # generated once, mode 600
   install.conf          # installer state
   backups/              # pre-update database snapshots
+  backups-archives/     # whole-data archives, from Settings > Backups
   data/
     db/cobble
     db/.backups/
@@ -213,6 +214,16 @@ Edit `.env` and run `docker restart cobble` to apply changes. The installer
 only appends missing values and keeps what is already there, apart from the
 port it manages.
 
+Settings > Backups makes two kinds of copy. Database snapshots (bun-sqlite's
+`backup` command) stay in `data/db/.backups` and can be restored from the
+app. Whole-data archives are a `tar.gz` of the entire `data/` directory,
+written to `backups-archives/` (mounted at `/backups-archives`, the
+`BACKUP_ARCHIVE_DIR` setting); every entry sits under one folder named after
+the archive, so extracting one by hand drops a single folder. Each group
+can create a copy, restore from one (a listed row, or a file uploaded from
+the button beside Create), download it and delete it; the newest five
+archives are kept.
+
 The app container is started with the Docker socket mounted and
 `MAIN_SERVER=1`, so it can create computer containers and run cron, the
 queue and Web Push.