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/Transceiver.h

@@ -87,7 +87,7 @@ class Transceiver {
     void beginFrequencyScan();
     void endFrequencyScan();
     void processFrequencyScan(bool received = false);
-    void emitFrequencyScan(uint8_t num = 255);
+    void emitFrequencyScan();
     bool usesPin(uint8_t pin);
 };
 // Bit length the radio was last set up for.  A frame sent without one