feat!: remove the old API, ports 8081 and 8080 (step 4a)

Step 4a of docs/SECURITY_PLAN.md. Port 80 keeps the eleven HTTP routes of
ADR 0006 and the socket at /ws; everything else moved to protocol 2.

- Port 8081 (ApiRoutes) and the socket on 8080 (SocketEmitter) are gone.
  Protocol 2 owns its frame buffer and loop-task check.
- Port 80 drops every route the old web UI called: reads, edits,
  settings, scans, reboot, /shades.cfg, /discovery. HttpRoutes.cpp holds
  what stays.
- ModelSnapshot, SnapshotSlots and the read documents are gone. The item
  snapshot types stay, as ItemSnapshot, for events, MQTT and the command
  replies.
- Model edits reply only to their protocol 2 op: requestResult goes.
- The settings' toJSON writers, used only by the settings routes, go.
- The _espsomfy_rts._tcp mDNS record moves to port 80, with path=/ws.
- The memory event reports the loop-rate window it closes.
- A deleted room no longer re-publishes its retained MQTT topics.
- e2e: the heap check reads the sync's status; the sync is checked on
  its own instead of against /controller.
- README gets an API and ports section.

BREAKING CHANGE: ports 8081 and 8080 and the old HTTP routes are gone.
Home Assistant needs integration 3.0.0 or newer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ModelEditor.h

@@ -23,7 +23,7 @@ enum class model_edit_type_t : uint8_t {
   set_paired,
   room_order, shade_order, group_order
 };
-// What an edit did, sent to the clients as requestResult.  id is the room,
+// What an edit did, sent in the edit op's reply.  id is the room,
 // shade or group it added or changed, 0 when none.  shadeId is the shade a
 // group gained or lost.  code is the validation error of a shade that wasn't
 // saved, 0 otherwise.  notFound: it was refused for an id that doesn't exist.