route-proxy: the trust step skips the fetch when the CA names no roots to get

Composed ACME_ROOTS unconditionally from ${bound:acme-ca:roots} even when
that field is empty — public-acme's own case, where an empty roots means
'the system trust store', not 'fetch from the bare authority host'. The
run-once step wget'd https://acme-v02.api.letsencrypt.org:443 (host, no
path) for two minutes every apply and failed, blocking every resource
after it — found live tonight, assigning route-proxy for the first time.

Carries the raw, uncomposed roots value alongside the composed URL
(ACME_ROOTS_PATH) so the step can tell 'nothing to fetch' apart from 'the
authority didn't answer' — a distinction the composed URL alone cannot
make. Empty copies the image's own system CA bundle to /ca/root.crt
instead of fetching one, so ACME_CA_BUNDLE stays the one path it has
always been rather than needing to become conditional itself.

modules/route-proxy/module.json

@@ -67,7 +67,7 @@
       "type": "file",
       "path": "/var/lib/route-proxy/acme.env",
       "mode": "0600",
-      "content": "ACME_DIRECTORY=https://${bound:acme-ca:at}:${bound:acme-ca:port}${bound:acme-ca:path}\nACME_ROOTS=https://${bound:acme-ca:at}:${bound:acme-ca:port}${bound:acme-ca:roots}\n"
+      "content": "ACME_DIRECTORY=https://${bound:acme-ca:at}:${bound:acme-ca:port}${bound:acme-ca:path}\nACME_ROOTS=https://${bound:acme-ca:at}:${bound:acme-ca:port}${bound:acme-ca:roots}\nACME_ROOTS_PATH=${bound:acme-ca:roots}\n"
     },
     {
       "id": "trust",
@@ -85,7 +85,7 @@
       "args": [
         "sh",
         "-c",
-        "for i in $(seq 1 60); do wget -q -T 10 --no-check-certificate -O /ca/root.crt \"$ACME_ROOTS\" && grep -q 'BEGIN CERTIFICATE' /ca/root.crt && exit 0; sleep 2; done; echo \"the authority at $ACME_ROOTS did not serve its roots within two minutes\" >&2; exit 1"
+        "if [ -z \"$ACME_ROOTS_PATH\" ]; then cp /etc/ssl/certs/ca-certificates.crt /ca/root.crt; exit 0; fi; for i in $(seq 1 60); do wget -q -T 10 --no-check-certificate -O /ca/root.crt \"$ACME_ROOTS\" && grep -q 'BEGIN CERTIFICATE' /ca/root.crt && exit 0; sleep 2; done; echo \"the authority at $ACME_ROOTS did not serve its roots within two minutes\" >&2; exit 1"
       ],
       "restart-on": [
         "acme-env"