feat(sprint-5): Phase 7 — System test harness

- docker-compose.test.yml: full stack test profile with seed + playwright
- scripts/seed/init.sql: test data (admin, members, batches, distributions)
- scripts/seed/seed.sh: backend readiness validation script
- e2e/system-test.spec.ts: full user journey against real/mock stack
- package.json: test:e2e, test:system, test:all scripts
- scripts/README.md: system test documentation and usage instructions

cannamanage-frontend/package.json

@@ -13,7 +13,10 @@
     "start": "next start",
     "lint": "next lint",
     "lint:fix": "next lint --fix",
-    "format": "prettier --ignore-path .gitignore --write ."
+    "format": "prettier --ignore-path .gitignore --write .",
+    "test:e2e": "playwright test e2e/full-check.spec.ts e2e/functional-flows.spec.ts",
+    "test:system": "playwright test e2e/system-test.spec.ts",
+    "test:all": "playwright test"
   },
   "engines": {
     "node": ">=22",