ci(deploy): make API-domain reconciliation opt-in, document the real host layout

The Reconcile tenant API domains step ran on every push to main. On the
production host that is actively harmful: api.gorbushka.market already has
a hand-written vhost, and configure-api-domain.sh writes its own file per
domain - so the step would hand nginx a second server block for a
server_name that already has one and re-run certbot against a live API,
once per deploy. Shipping frontend files needs none of it. Gate it behind
a workflow_dispatch input, off by default, for standing up a NEW base
domain.

This also shrinks the secrets a normal deploy requires to four
(DEPLOY_HOST, DEPLOY_USER, DEPLOY_SSH_KEY, DEPLOY_KNOWN_HOSTS);
STOREFRONT_DOMAINS, CERTBOT_EMAIL and BACKEND_UPSTREAM are now read only
on the opt-in path.

Document the production host as it actually is: provisioned by hand before
server-setup.sh existed, per-domain vhosts rooted at
/var/www/dexarmarket/browser, which is now a symlink to
/srv/marketplaces/current/frontend. Before 2026-08-22 it pointed straight
at a pinned release with no `current` in between, so releases 14d46ce and
98c39f6 uploaded successfully and were never served.

.github/workflows/deploy.yml

@@ -13,6 +13,15 @@ on:
         description: Branch or SHA to deploy
         required: false
         default: main
+      reconcile_api_domains:
+        description: >-
+          Also provision api.<base-domain> nginx vhosts and TLS. Off by default:
+          existing API domains are configured by hand, and re-running the helper
+          writes a second server block for a server_name that already has one.
+          Turn this on only when adding a NEW base domain.
+        type: boolean
+        required: false
+        default: false
 
 concurrency:
   group: deploy-frontend
@@ -82,7 +91,13 @@ jobs:
           printf '%s\n' "$DEPLOY_KNOWN_HOSTS" > ~/.ssh/known_hosts
           chmod 644 ~/.ssh/known_hosts
 
+      # Opt-in only. api.<base-domain> vhosts already exist and are hand-managed;
+      # the helper writes its own file per domain, so running it unconditionally
+      # would give nginx two server blocks for one server_name and re-run certbot
+      # against a live API on every single deploy. Frontend releases do not need
+      # this step - it is for standing up a NEW base domain.
       - name: Reconcile tenant API domains
+        if: ${{ inputs.reconcile_api_domains }}
         env:
           HOST: ${{ secrets.DEPLOY_HOST }}
           USER: ${{ secrets.DEPLOY_USER }}