Let the extension update itself, and host the dashboard

Chrome has no update channel for an unpacked extension, so every pull left one
manual step: click reload on its card. The dashboard now publishes the version
its own checkout ships at /api/autobuyer/status, and the extension reloads
itself when it is behind — chrome.runtime.reload() re-reads the folder from
disk, which the update check has already pulled into. It only ever runs code
that is on disk, so a reload that changes nothing is reported and waited out
rather than repeated; a dashboard that is behind is ignored.

Also adds the deploy stack for running the dashboard on the droplet, next to
the autotrader one: it joins that nginx's network and renders a server block
into its conf.d rather than standing up a second ingress. AUTOFIRMER_DB moves
the SQLite file onto a volume, since the working directory in a container is
replaced on every deploy.

And waitFor gained `hidden`: an absent gate matched on DOM presence only, so a
modal that closes by going display:none could never satisfy it. The extension
grew a visibility probe for this — locate cannot answer it, because absent and
hidden are both errors there and a wait gate has to tell them apart.

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

deploy/nginx/firmer-acme.conf.template

@@ -0,0 +1,16 @@
+# HTTP only, for the window before a certificate exists: nginx will not start
+# with an ssl_certificate that is not on disk yet, so the real config cannot go
+# in until certbot has run. Rendered by bootstrap-tls.sh.
+server {
+    listen 80;
+    listen [::]:80;
+    server_name ${FIRMER_HOST};
+
+    location /.well-known/acme-challenge/ {
+        root /var/www/certbot;
+    }
+
+    location / {
+        return 503;
+    }
+}