plex: probe the readiness gate over HTTPS — PMS drops plain HTTP off-loopback

deploy_plex gated on `curl http://127.0.0.1:32400/identity`, which can never
succeed: Plex accepts the TCP connection (it arrives on the container's eth0)
and then answers with nothing, so curl reports "Empty reply from server" (52).
Measured 2026-10-02 on a plex that was healthy the whole time —
`https://127.0.0.1:32400/identity` returned 200 in 44 ms while the gate burned
its full 600 s and failed the deploy.

The repo already knew this law in another place: tests/caddyfile.bats pins the
plex vhosts to a TLS upstream with the comment "PMS drops plain HTTP
off-loopback". The deployer's gate never got the same treatment, and plex's
per-service revision had been behind long enough that the gate had not run
against this posture until now.

-k because PMS serves its own self-signed cert on 32400.

scripts/deploy-remote.sh

@@ -935,15 +935,24 @@ deploy_plex() {
     fi
     systemctl --user restart plex.service
     # Readiness gate: /identity answers MediaContainer XML once PMS is up.
+    #
+    # HTTPS, NOT HTTP. PMS drops plain HTTP off-loopback: the probe's
+    # connection arrives on the container's eth0, so an http:// request is
+    # accepted and then answered with nothing (curl 52, Empty reply) against a
+    # perfectly healthy server. Measured 2026-10-02 — the gate burned its full
+    # 600s and failed a plex whose https://127.0.0.1:32400/identity answered
+    # 200 in 44 ms the whole time. The same law is why the Caddyfile dials the
+    # plex upstream over TLS (tests/caddyfile.bats pins it).
+    # -k: PMS presents its own self-signed cert on 32400.
+    #
     # Reality check from the 2026-09 cutover: the FIRST container boot of a
-    # years-old library ran ~10 min (PMS pre-binds 32400 during boot and
-    # empty-replies until the HTTP layer is ready), so the gate allows 600s.
+    # years-old library ran ~10 min, so the gate still allows 600s.
     # Fail the deploy (pending state preserved) rather than mark it deployed blind.
     for ((i = 1; i <= 120; i++)); do
-        curl -fsS --max-time 3 http://127.0.0.1:32400/identity >/dev/null && return 0
+        curl -fsSk --max-time 3 https://127.0.0.1:32400/identity >/dev/null && return 0
         sleep 5
     done
-    echo "FAIL: plex did not answer /identity within 600s" >&2
+    echo "FAIL: plex did not answer /identity over HTTPS within 600s" >&2
     return 1
 }