fix: protocol 2 core review findings

From the review of #99:
- A sync could stall when a client took a slot the moment another left:
  loop() used up the new client's sync on the old one. The slots move
  to ProtoSlots, a pure module with native tests, and loop() takes a
  slot's wants only for the client it read (takeWants).
- Deleting a group sends its shades, whose inGroup changed. Deleting a
  shade unlinks it from its groups and sends them, so a new shade given
  its id doesn't join them.
- next and sync with an id get an ok reply, and a message in pieces
  gets one bad request, not one per piece.
- Feeds check for loop() before they write the event buffer, and log
  an event too large, as events do.
- editChanges() (ModelEditor, native tests) says what clients get after
  an edit; the edit result carries the shade a group gained or lost.
  order() takes a sort_list_t.
- The frame writers move to ProtoFrame. Renames: pf to proto_field_t,
  the X-macro letters to TYPE/FIELD/ERR/FEED, proto_request_t to
  proto_message_t, REQ_* to WANTS_*, fmt to eventJson. The event
  bodies share sendItem(), the connection type name lives in
  ESPNetwork, and the loop() task check in SocketEmitter.
- e2e: the heap floor check skips when the low since boot is already
  under it; tests for replies to next and sync and a long message.
- SECURITY_PLAN.md splits step 1 into 1a-1d.

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

src/entryPoints/Web.cpp

@@ -231,9 +231,6 @@ static void controllerHeader(JsonFormatter &json, const model_snapshot_t &snap)
 // The parts of /discovery that aren't in the shade model.
 static void discoveryHeader(JsonFormatter &json, const model_snapshot_t &snap) {
   (void)snap;
-  const char *connType = "Unknown";
-  if(net.connType == conn_types_t::ethernet) connType = "Ethernet";
-  else if(net.connType == conn_types_t::wifi) connType = "Wifi";
   json.addElem("serverId", settings.serverId);
   json.addElem("version", settings.fwVersion.name);
   json.addElem("model", "ESPSomfyRTS");
@@ -241,7 +238,7 @@ static void discoveryHeader(JsonFormatter &json, const model_snapshot_t &snap) {
   json.addElem("authType", static_cast<uint8_t>(settings.Security.type));
   json.addElem("permissions", settings.Security.permissions);
   json.addElem("chipModel", settings.chipModel);
-  json.addElem("connType", connType);
+  json.addElem("connType", net.connTypeName());
   json.beginObject("memory");
   json.addElem("max", ESP.getMaxAllocHeap());
   json.addElem("free", ESP.getFreeHeap());