docs(19-04): mark ChatChannels API plan complete on the roadmap

Co-authored-by: Cursor <cursoragent@cursor.com>

.planning/ROADMAP.md

@@ -1198,7 +1198,7 @@ Plans:
   3. Golden tests show that the serializers (`Message.toApiArray` with attachments, thread summaries, channel, category, pref, pin and mention arrays) and every realtime event (name, channel and payload) match PHP output captured from Wavepath. Route-level parity of `/_wave` is checked at the Wavepath port.
   4. The new code has unit tests, delivered in the phase's last plan.
 
-**Plans:** 3/5 plans executed
+**Plans:** 4/5 plans executed
 
 Plans:
 **Wave 1**
@@ -1209,7 +1209,7 @@ Plans:
 - [x] 19-03-PLAN.md — ChatChannels core: new sm-chatchannels-plugin repo, baseline, ChannelService, festival listeners, beachcomber search
 
 **Wave 3** *(blocked on Wave 2)*
-- [ ] 19-04-PLAN.md — ChatChannels generic API + sm-user-plugin handle, user authorizer, lifecycle events
+- [x] 19-04-PLAN.md — ChatChannels generic API + sm-user-plugin handle, user authorizer, lifecycle events
 
 **Wave 4** *(blocked on Wave 3)*
 - [ ] 19-05-PLAN.md — Unit tests LAST: goldens, PHP method map (59 chat + 106 chatchannels), scripts/check-phase19.sh
@@ -1417,7 +1417,7 @@ Phases execute in numeric order: 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8 →
 | 17. Blog companions | 6/6 | Complete   | 2026-10-13 |
 | 18. Payment Gateway | 8/8 | Complete   | 2026-10-14 |
 | 18.1. Payment Gateway Subscriptions | 9/9 | Complete    | 2026-10-16 |
-| 19. Chat and ChatChannels | 3/5 | In Progress|  |
+| 19. Chat and ChatChannels | 4/5 | In Progress|  |
 | 19.1. Chat satellites | 0/TBD | Not started | - |
 | 19.2. Chat polish against WavePath clients | 0/TBD | Not started | - |
 | 19.3. Framework transport and infrastructure for WavePath | 6/6 | In Progress|  |