Admin-scoped user accounts, secure qr code storage, PHP 8.4 upgrade

Admin-scoped users (answers: who can create a 'user' account, only super or
also an admin within their own scope?):
- New owner_admin_id column on users (migration 004). NULL means created by
  super (company-wide, previous behavior); otherwise scoped to that admin's
  own codes.
- Users::addUser/editUser/deleteUser now allow an 'admin' session, but force
  type='user' and owner_admin_id to their own id regardless of submitted
  input. user.php/users.php open up to admins with a restricted UI (no type
  picker, listing limited to their own created users).
- New qr_compute_scope_owner_id()/qr_apply_owner_scope()/qr_has_full_visibility()
  helpers in includes/security.php, replacing the ad-hoc type==='admin' checks
  in index.php, dynamic_qrcodes.php, static_qrcodes.php and bulk_action.php.
  A 'user' account created by an admin is now scoped to that admin's codes
  instead of seeing everything company-wide.

Qr code storage hardening: images were served as plain static files under the
document root with no auth check at all. Storage now lives outside the web
root; qrcode_image.php and qrcode_zip_download.php gate access with the same
permission model as the list pages, and the bulk zip download is bound to the
session that generated it.

PHP 8.4 + chillerlan/php-qrcode 6.0.1: bumped since this is a dockerized app,
so the PHP version shipped doesn't matter to end users. Note: the 6.0.1 tag
itself only requires PHP 8.2 - the earlier "needs 8.4" read was from an
unpinned clone of master, which has since moved past the tag. Fixed along the
way, surfaced by testing on 8.4:
- The hardcoded Imagick build (an old pinned master commit, workaround for
  3.7.0 being broken on PHP 8.3+) no longer compiles on 8.4. Imagick 3.8.1 is
  now a normal stable release, so the workaround is gone.
- config.php had display_errors=On + error_reporting(E_ALL), so PHP 8.4's new
  deprecation notices got dumped straight into the response before
  session_start() could run, breaking login outright. Also an info-disclosure
  risk on its own. Now logged instead of displayed.
- MysqliDb::insertMulti() had an implicit nullable parameter, now explicit.
- includes/auth_validate.php redirected unauthenticated requests but never
  called exit(), so the rest of the script kept running.
- Dockerfile.fpm was missing both git (needed to clone chillerlan/php-qrcode)
  and the imagick extension entirely.

Also removes the unused sample qr code images that shipped in the original
repo; storage now lives outside the document root so they were never going
to be served again.

docker-compose.prod.yml

@@ -4,11 +4,10 @@ services:
     restart: "unless-stopped"
     ports:
       - "80:80"
-      # 443 pas openzetten zodra SSL-certificaten zijn gemount (bv. via certbot-volume
-      # of een losse reverse proxy zoals Caddy/Traefik ervoor). Zie infra-fase van het plan.
+      # Only open 443 once SSL certificates are mounted (e.g. via a certbot volume,
+      # or a separate reverse proxy like Caddy/Traefik in front). See the infra phase of the plan.
     volumes:
       - ./nginx.conf:/etc/nginx/conf.d/default.conf:ro
-      - php_dynamic_qrcode_saved_qrcode_data:/var/www/html/saved_qrcode:ro
     depends_on:
       - php-dynamic-qrcode
     networks:
@@ -22,19 +21,19 @@ services:
     environment:
       TYPE: "docker"
       QRCODE_GENERATOR: "${QRCODE_GENERATOR:-internal-chillerlan.qrcode}"
-      BASE_URL: "${BASE_URL:?zet BASE_URL in .env, bv. https://qr.ensembia.com}"
+      BASE_URL: "${BASE_URL:?set BASE_URL in .env, e.g. https://qr.ensembia.com}"
       DATABASE_HOST: "php-dynamic-qrcode-db"
       DATABASE_PORT: "3306"
       DATABASE_NAME: "${DATABASE_NAME:-qrcode}"
       DATABASE_USER: "${DATABASE_USER:-qrcode}"
-      DATABASE_PASSWORD: "${DATABASE_PASSWORD:?zet DATABASE_PASSWORD in .env}"
+      DATABASE_PASSWORD: "${DATABASE_PASSWORD:?set DATABASE_PASSWORD in .env}"
       DATABASE_PREFIX: "${DATABASE_PREFIX:-}"
       DATABASE_CHARSET: "${DATABASE_CHARSET:-utf8}"
     depends_on:
       php-dynamic-qrcode-db:
         condition: service_healthy
     volumes:
-      - php_dynamic_qrcode_saved_qrcode_data:/var/www/html/saved_qrcode
+      - php_dynamic_qrcode_saved_qrcode_data:/var/www/qrcode-storage
     networks:
       - php-dynamic-qrcode-network
 
@@ -45,10 +44,10 @@ services:
       - php_dynamic_qrcode_db_data:/var/lib/mysql
       - ./db/init.sql:/docker-entrypoint-initdb.d/init.sql:ro
     environment:
-      MYSQL_ROOT_PASSWORD: "${MYSQL_ROOT_PASSWORD:?zet MYSQL_ROOT_PASSWORD in .env}"
+      MYSQL_ROOT_PASSWORD: "${MYSQL_ROOT_PASSWORD:?set MYSQL_ROOT_PASSWORD in .env}"
       MYSQL_DATABASE: "${DATABASE_NAME:-qrcode}"
       MYSQL_USER: "${DATABASE_USER:-qrcode}"
-      MYSQL_PASSWORD: "${DATABASE_PASSWORD:?zet DATABASE_PASSWORD in .env}"
+      MYSQL_PASSWORD: "${DATABASE_PASSWORD:?set DATABASE_PASSWORD in .env}"
     healthcheck:
       test: ["CMD", "mysqladmin", "ping", "-h", "localhost", "-u", "root", "-p${MYSQL_ROOT_PASSWORD}"]
       interval: 5s