build(deps): Bootstrap and Bootswatch 5.3.8

Bootstrap SCSS, the JS bundle and the Bootswatch themes go from 5.3.3 to
5.3.8 (bug fixes only), and wvc-main.min.css is recompiled from zephyr.
Bootswatch now gives table text the body color, and Lux drops card and
modal header borders.

Tests compile every theme with the pinned libsass and check that the
shipped CSS is zephyr from these sources. The update and rollback steps
put back the two files a theme change rewrites, or git refuses to pull
over them.

README.md

@@ -444,6 +444,7 @@ docker compose up -d
    venv/bin/python3 -c "import sqlite3,sys; sqlite3.connect('db.sqlite3').backup(sqlite3.connect(sys.argv[1]))" "$b/db.sqlite3" &&
    cp -p webvirtcloud/settings.py /etc/nginx/conf.d/webvirtcloud.conf "$b"/ &&
    git rev-parse HEAD > "$b/commit" &&
+   git checkout -- static/css/wvc-main.min.css dev/scss/wvc-main.scss &&
    git checkout master && git pull
    ```
 
@@ -507,6 +508,7 @@ b=/root/webvirtcloud-backup-YYYYMMDD-HHMMSS
 supervisorctl stop webvirtcloud novncd
 cd /srv/webvirtcloud &&
 ! supervisorctl status webvirtcloud novncd | grep RUNNING &&
+git checkout -- static/css/wvc-main.min.css dev/scss/wvc-main.scss &&
 git checkout "$(cat "$b/commit")" &&
 venv/bin/python3 -c "import os,sqlite3,sys; [os.remove(p) for p in ('db.sqlite3-journal','db.sqlite3-wal','db.sqlite3-shm') if os.path.exists(p)]; sqlite3.connect(sys.argv[1]).backup(sqlite3.connect('db.sqlite3'))" "$b/db.sqlite3" &&
 cp "$b/settings.py" webvirtcloud/settings.py &&
@@ -552,6 +554,7 @@ A rollback leaves the clone on a detached HEAD at the restored commit; the updat
 - A running VM without a guest agent shows the IPv4 address the host learned by ARP (the lookup always failed before).
 - After a live migration the VM's NVRAM file is deleted on the source, when it is in libvirt's `/var/lib/libvirt/qemu/nvram` and the destination does not share that directory (a VM created there later with the same name would start with those UEFI variables).
 - gstfsd finds the guest's operating system the way libguestfs inspects it, so a root on LVM works, and it always answers (an error when it finds no or several operating systems). Update `/usr/local/bin/gstfsd` on every compute (see [Adding a Compute Node](#adding-a-compute-node), step 3).
+- A theme picked on the Settings page rewrites two tracked files; the update and rollback steps put back the shipped theme. Pick yours again afterwards, also after Docker recreates the container.
 - Docker no longer publishes port 6080; the console goes through nginx on the panel's port (`WS_PUBLIC_PORT`, default 80).
 
 ## Usage