fix(ssh): per-challenge SSH login + phew buffering/leak/timeout

Passwords failed on 10/16 challenges while state.json looked correct:
- only the 6 native GEMASTIK XVIII images provision 'ctfuser'; every imported
  XVI/XVII image does 'echo root:${PASSWORD} | chpasswd' and logs in as root.
  set_ssh_passwords() hardcoded ctfuser, so chpasswd set a password on an
  account nobody uses -> 'Permission denied' everywhere.
  Registry gains a per-challenge 'ssh_user'; chpasswd now targets the real
  login (and ctfuser/ctf when present) and reports failures loudly.
- phew checker: chall.py block-buffers stdout through the docker exec pipe
  (PYTHONUNBUFFERED now set) and leaks chall.py inside the container on
  timeout (26 orphans, container saturated) -> reaps the whole exec process
  group. Startup does a fresh Pailier keygen (~12 s) so crypto reads need
  _CRYPTO_TIMEOUT, not the 5 s prompt default.

Adds panel/verify_ssh_creds.py (proves the state->container binding from
inside via a real login), audit_ssh_users.sh, reset_runtime.sh.

panel/apply_registry.sh

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+# Bring every team's containers in line with the registry's enabled set.
+#
+# For each team: re-render the compose from the registry, then `up -d`. Because
+# the shared `services-<name>` images already exist, this is a start, not a
+# rebuild, so it is fast. Containers of challenges that are no longer enabled are
+# removed by `up --remove-orphans`.
+set -uo pipefail
+cd /opt/gemastik18-final/panel
+python3 - <<'PY'
+import json, sys
+sys.path.insert(0, '.')
+import teams as orch, compose_gen
+orch.reconcile_team_state()
+for d in sorted(orch.TEAMS_DIR.glob("team*")):
+    sf = d / "state.json"
+    if not sf.exists():
+        continue
+    st = json.loads(sf.read_text())
+    (d / "services" / "docker-compose.yml").write_text(
+        compose_gen.render_team_compose(st["index"], st))
+    print(f"team{st['index']} compose rendered")
+PY
+
+for i in 1 2 3 4; do
+  cd "/opt/gemastik18-final/teams/team$i/services"
+  echo "--- team$i ---"
+  docker compose -p "team$i" up -d --remove-orphans 2>&1 | tail -2
+done
+
+echo "=== result ==="
+docker ps --format '{{.Names}}' | grep -c '_container_team'
+df -h / | tail -1