🚧 Update topic explorer

README.md

@@ -203,11 +203,16 @@ Hardening done beyond the plan:
       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
+- [x] Topic explorer: consolidated topic view (spec §35.1) — one row
+      per known topic (messages folded as they arrive); changed cells
+      (payload, QoS, retain, MQTT 5 properties) highlighted against the
+      previous message; changed tokens WITHIN a text payload highlighted
+      word-level (jsdiff diffWords — e.g. `{"cmd": "start"}` →
+      `{"cmd": "stop"}` marks only `stop`); fallbacks to plain text for
+      a topic's first message, binary payloads, and payloads >4 KB; row
+      glows briefly on new-message arrival; per-topic history browsable
+      (most recent first, per-topic ring buffer of 100 in the UI,
+      session buffer of 1000 server-side)
 - [ ] Connection tester + client provisioning wizard
 - [ ] Bridge configuration
 - [ ] Retained-message administration (partially covered by the topic