feat(phase4): add Phase 4 standalone lab test script (25/25 PASS)

lab-phase4.sh: 25-test runner for Phase 4 standalone labs (Lab XX-01)
- Lab 05-01 Elasticsearch  5/5 PASS  (cluster health, index CRUD)
- Lab 16-01 Snipe-IT       4/4 PASS  (MariaDB, HTTP, branding)
- Lab 17-01 GLPI           4/4 PASS  (MariaDB, HTTP, branding)
- Lab 19-01 Zabbix         4/4 PASS  (PostgreSQL, web UI, API jsonrpc)
- Lab 15-01 Taiga          4/4 PASS  (PostgreSQL, back API, front nginx)
- Lab 20-01 Graylog        5/5 PASS  (MongoDB, Elasticsearch, lbstatus)

Patterns: wait_http direct polling for slow-starting apps (Taiga),
vm.max_map_count=262144 for Elasticsearch, GRAYLOG_MESSAGE_JOURNAL_MAX_SIZE=512mb
for disk-constrained labs, --skip/--only flags per module.

Tested on: Azure VM lab-single (Ubuntu 24.04, 16GB RAM, 29GB disk)
Verified: all 25 tests pass across targeted module runs

Author: RedjiJB