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/ProtoParse.cpp

@@ -1,7 +1,7 @@
 #include "ProtoParse.h"
 
-proto_error_t parseClientFrame(const char *text, size_t len, JsonDocument &doc, proto_request_t &out) {
-  out = proto_request_t();
+proto_error_t parseClientFrame(const char *text, size_t len, JsonDocument &doc, proto_message_t &out) {
+  out = proto_message_t();
   if(len > PROTO_MAX_CLIENT_FRAME) return proto_error_t::badRequest;
   if(deserializeJson(doc, text, len) != DeserializationError::Ok) return proto_error_t::badRequest;
   if(!doc.is<JsonObject>()) return proto_error_t::badRequest;
@@ -19,18 +19,18 @@ proto_error_t parseClientFrame(const char *text, size_t len, JsonDocument &doc,
   return proto_error_t::none;
 }
 
-int32_t protoInt(JsonObjectConst d, pf field) {
+int32_t protoInt(JsonObjectConst d, proto_field_t field) {
   const proto_field_info_t &f = protoField(field);
   JsonVariantConst v = d[f.key];
   return v.is<int32_t>() ? v.as<int32_t>() : f.def;
 }
-bool protoBool(JsonObjectConst d, pf field) {
+bool protoBool(JsonObjectConst d, proto_field_t field) {
   const proto_field_info_t &f = protoField(field);
   JsonVariantConst v = d[f.key];
   return v.is<int>() ? v.as<int>() != 0 : f.def != 0;
 }
-const char *protoString(JsonObjectConst d, pf field) {
+const char *protoString(JsonObjectConst d, proto_field_t field) {
   JsonVariantConst v = d[protoField(field).key];
   return v.is<const char *>() ? v.as<const char *>() : nullptr;
 }
-bool protoHas(JsonObjectConst d, pf field) { return !d[protoField(field).key].isNull(); }
+bool protoHas(JsonObjectConst d, proto_field_t field) { return !d[protoField(field).key].isNull(); }