Fix authentik-setup.sh: broken jget stdin handling, wrong stage path

Two bugs found running this against the live Authentik instance for
the first time:

- jget's <<<"$1" here-string always overrode stdin, so `api ... | jget
  - "expr"` never actually read curl's piped output - it fed the
  literal string "-" to json.load() instead, and the abandoned pipe
  made curl fail with "Failed writing body". Fixed by branching on
  $1 == "-" to read the real stdin in that case.
- The prompt stage lives at /stages/prompt/stages/, not /stages/prompt/
  (that path is prompt *fields*). Wrong path 404'd.

Also switched `python` -> `python3` throughout for portability.

Verified idempotent end-to-end against auth.jerodrigged.com: provider,
application, lisilou-admin group, and the full enrollment flow
(prompt -> write -> login stages, bound and set as the brand's
enrollment flow) all created successfully, second run reports
everything as already existing.

scripts/authentik-setup.sh

@@ -39,7 +39,13 @@ api() { # method path [json-body]
   fi
 }
 
-jget() { python -c "import sys,json;d=json.load(sys.stdin);print(eval(sys.argv[1]))" "$2" <<<"$1"; }
+jget() { # jget <json-string|-> <python-expr>  ('-' reads JSON from stdin, e.g. a pipe)
+  if [ "$1" = "-" ]; then
+    python3 -c "import sys,json;d=json.load(sys.stdin);print(eval(sys.argv[1]))" "$2"
+  else
+    python3 -c "import sys,json;d=json.load(sys.stdin);print(eval(sys.argv[1]))" "$2" <<<"$1"
+  fi
+}
 
 echo "── Checking API access…"
 VERSION=$(api GET /admin/version/ | jget - "d['version_current']" 2>/dev/null || true)
@@ -54,7 +60,7 @@ SCOPES=$(api GET "/propertymappings/provider/scope/?managed__iexact=goauthentik.
 for s in profile email; do
   SCOPES="$SCOPES,$(api GET "/propertymappings/provider/scope/?managed__iexact=goauthentik.io/providers/oauth2/scope-$s" | jget - "d['results'][0]['pk']")"
 done
-SCOPES_JSON=$(python -c "import sys;print(__import__('json').dumps(sys.argv[1].split(',')))" "$SCOPES")
+SCOPES_JSON=$(python3 -c "import sys;print(__import__('json').dumps(sys.argv[1].split(',')))" "$SCOPES")
 
 # ── 2. OAuth2 provider ────────────────────────────────────────────────────────
 echo "── Provider…"
@@ -63,7 +69,7 @@ if [ "$EXISTING" -gt 0 ]; then
   PROVIDER_PK=$(api GET "/providers/oauth2/?name=$CLIENT_ID" | jget - "d['results'][0]['pk']")
   echo "   exists (pk=$PROVIDER_PK)"
 else
-  BODY=$(python - "$AUTHZ_FLOW" "$INVALIDATION_FLOW" "$SCOPES_JSON" <<'PY'
+  BODY=$(python3 - "$AUTHZ_FLOW" "$INVALIDATION_FLOW" "$SCOPES_JSON" <<'PY'
 import json, sys
 authz, inval, scopes = sys.argv[1], sys.argv[2], json.loads(sys.argv[3])
 p = {
@@ -85,7 +91,7 @@ PY
 )
   RESP=$(api POST /providers/oauth2/ "$BODY" 2>&1) || {
     # Older Authentik (<2024.2) wants redirect_uris as a newline-joined string
-    BODY=$(python -c "
+    BODY=$(python3 -c "
 import json,sys
 p=json.loads(sys.argv[1]); p['redirect_uris']='\n'.join(u['url'] for u in p['redirect_uris']); print(json.dumps(p))" "$BODY")
     RESP=$(api POST /providers/oauth2/ "$BODY")
@@ -155,7 +161,7 @@ else
   make_field password "Password" password 3 ""
   make_field password_repeat "Confirm password" password 4 ""
 
-  PROMPT_STAGE=$(api POST /stages/prompt/ "{
+  PROMPT_STAGE=$(api POST /stages/prompt/stages/ "{
     \"name\": \"lisilou-enrollment-prompt\",
     \"fields\": [\"${FIELD_PKS[username]}\",\"${FIELD_PKS[name]}\",\"${FIELD_PKS[email]}\",\"${FIELD_PKS[password]}\",\"${FIELD_PKS[password_repeat]}\"]
   }" | jget - "d['pk']")
@@ -191,7 +197,7 @@ OIDC_CLIENT_ID=$CLIENT_ID
 OIDC_CLIENT_SECRET=$CLIENT_SECRET
 OIDC_REDIRECT_URI=$PROD_REDIRECT
 OIDC_ADMIN_GROUP=lisilou-admin
-SESSION_SECRET=$(openssl rand -hex 32 2>/dev/null || python -c "import secrets;print(secrets.token_hex(32))")
+SESSION_SECRET=$(openssl rand -hex 32 2>/dev/null || python3 -c "import secrets;print(secrets.token_hex(32))")
 
 Then: docker compose restart api
 EOF