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/Somfy.h

@@ -140,6 +140,8 @@ class SomfyShade : public SomfyRemote, public ShadeSettings, private MotorLink,
     void emitState(uint8_t num, const char *evt = "shadeState");
     // What changed since the fan-out last sent the shade (SHADE_CHANGED_* bits).
     uint16_t changed = 0;
+    // A setting changed: protocol 2 clients get the whole shade.
+    void configChanged() { this->changed |= SHADE_CHANGED_CONFIG; }
     void emitCommand(somfy_commands cmd, const char *source, uint32_t sourceAddress, const char *evt = "shadeCommand");
     void emitCommand(uint8_t num, somfy_commands cmd, const char *source, uint32_t sourceAddress, const char *evt = "shadeCommand");
     // False when the radio refused a command it sent.
@@ -215,6 +217,8 @@ class SomfyGroup : public SomfyRemote {
     void emitState(uint8_t num, const char *evt = "groupState");
     // What changed since the fan-out last sent the group (GROUP_CHANGED_* bits).
     uint8_t changed = 0;
+    // A setting or its shades changed: protocol 2 clients get the whole group.
+    void configChanged() { this->changed |= GROUP_CHANGED_CONFIG; }
     bool sendCommand(somfy_commands cmd);
     bool sendCommand(somfy_commands cmd, uint8_t repeat, uint8_t stepSize = 0);
     int8_t p_direction(int8_t dir);