feat(pki-server): add public PKI repository API

Add the disclosure-controlled public certificate, chain, CRL and status
repository with capability-based unlisted access, bounded streaming,
conditional caching and isolated public execution resources.

Introduce authoritative issuer generations and explicit chain paths so
issuance bundles and stable public chain routes never rely on inferred
certificate ordering or runtime path guessing.

docs/pki-server-trusted-proxy-nginx-example.json

@@ -1,5 +1,5 @@
 {
-  "version": 2,
+  "version": 3,
   "serverName": "zeroecho-admin-nginx",
   "realm": {
     "realmId": "production",
@@ -40,5 +40,6 @@
     "maximumForwardedChainBytes": 524288
   },
   "execution": {"transportWorkers":8,"transportQueueCapacity":64,"operationWorkers":4,"operationQueueCapacity":32,"maximumAdmittedRequests":96,"defaultDeadlineMillis":30000,"maximumDeadlineMillis":120000,"gracefulShutdownMillis":30000,"forcedShutdownMillis":10000},
+  "publicListener": {"enabled":false},
   "runtime": {}
 }