🚧 Add topic explorer

README.md

@@ -195,12 +195,23 @@ Hardening done beyond the plan:
 - [ ] Configuration drift detection (§48)
 - [ ] Last-known-connection tracking + connected-client view (§34)
 
-### Post-MVP (§68.4 / §69 / §70) — NOT STARTED
+### Post-MVP (§68.4 / §69 / §70) — PARTIAL
 
-- [ ] Topic explorer / MQTT test client
+- [x] Topic explorer (spec §35/§36): live message stream over SSE
+      (one MQTT v5 client per browser session, SUBACK-gated subscribe),
+      publish with QoS/retain (audited as TOPIC_PUBLISHED — metadata
+      only, never the payload), retained-message listing and clearing
+      (audited as RETAINED_CLEARED); RBAC: viewing = operator+,
+      publishing/clearing = broker-admin+ — verified live end-to-end
+- [ ] Topic explorer: consolidated topic view (spec §35.1) — one row
+      per known topic; highlight differences between the new and the
+      previous message per topic (payload, QoS, retain, MQTT 5
+      properties); briefly glow the row on new-message arrival;
+      browse the known history of each topic
 - [ ] Connection tester + client provisioning wizard
 - [ ] Bridge configuration
-- [ ] Retained-message administration
+- [ ] Retained-message administration (partially covered by the topic
+      explorer: listing + clearing; a dedicated §36 page can follow)
 - [ ] Certificate expiry alerts
 - [ ] Prometheus metrics + external notifications
 - [ ] Change approval (four-eyes) workflow