feat(audit): add audit log endpoint and display names from Auth

GET /api/library/audit-log for auditors and admins, paged, filter by
action. The account state push stores displayName in account_name so
the log shows names. Contract test updated.

src/test/resources/contract/auth-core-contract.json

@@ -37,12 +37,12 @@
     "applyStates": {
       "method": "POST",
       "path": "/internal/accounts/states",
-      "request": {"accounts": [{"userId": 42, "steamId": 76561198000000001, "blocked": true}]}
+      "request": {"accounts": [{"userId": 42, "steamId": 76561198000000001, "displayName": "lobo", "blocked": true}]}
     },
     "replaceStates": {
       "method": "PUT",
       "path": "/internal/accounts/states",
-      "request": {"accounts": [{"userId": 42, "steamId": null, "blocked": false}]}
+      "request": {"accounts": [{"userId": 42, "steamId": null, "displayName": "lobo", "blocked": false}]}
     },
     "purge": {
       "method": "POST",