fix: review fixes for step 4a

- e2e: the heap check uses a socket slot now, so it waits for the device
  to free it, and test_every_client_reconnecting_at_once closes its
  clients before the check runs.
- Comments and docs that still named removed things (the /controller read,
  the event buffer, memStatus, SocketEmitter, ModelSnapshot).
- ESPNetwork::emitSockets is emitStatus: one socket, and it sends the status.
- Unused includes, whitespace-only lines left by the toJSON removal.

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

docs/PROTOCOL.md

@@ -180,4 +180,4 @@ A malformed message gets a bad request, with its `id` when it had one. A type a
 
 ## Inside the device
 
-async_tcp reads client frames and answers with fixed frames that hold nothing of the shade model: `hello`, errors and `ok`. Everything formatted from the shade model goes out from `loop()`, which is the only task that reads and writes it ([ADR 0002](adr/0002-loop-task-is-the-only-writer-of-the-shade-model.md)). Sync frames and events share the socket event buffer, so protocol 2 needs no more static memory.
+async_tcp reads client frames and answers with fixed frames that hold nothing of the shade model: `hello`, errors and `ok`. Everything formatted from the shade model goes out from `loop()`, which is the only task that reads and writes it ([ADR 0002](adr/0002-loop-task-is-the-only-writer-of-the-shade-model.md)). Sync frames and events share one frame buffer, which belongs to `loop()`.

docs/adr/0002-loop-task-is-the-only-writer-of-the-shade-model.md

@@ -13,7 +13,7 @@ The shade model (rooms, shades, groups and repeaters) is changed only from `loop
 
 ## Consequences
 
-> **Amended by [ADR 0005](0005-one-websocket-protocol.md) (socket protocol 2).** The rule above stands. These consequences are replaced: model edits no longer answer "accepted" and report through `requestResult`, because every socket op gets one reply from `loop()`. Reads no longer go through a ModelSnapshot, because `loop()` formats a sync from the live model. The caps on reads and the UI's 5 s `requestResult` wait go with them.
+> **Amended by [ADR 0005](0005-one-websocket-protocol.md) (socket protocol 2).** The rule above stands. These consequences are replaced: model edits no longer answer "accepted" and report through `requestResult`, because every socket op gets one reply from `loop()`. Reads no longer go through a ModelSnapshot, because `loop()` formats a sync from the live model. The caps on reads and the UI's 5 s `requestResult` wait go with them, and 4.0.0 removes ModelSnapshot.
 
 - async_tcp must still never wait for `loop()`, so a model edit's HTTP reply can't block until the change is made. The reply only says the request was accepted; the result reaches clients as a WebSocket event once `loop()` has made the change. We chose that over a chunked HTTP response that `loop()` completes, because pushing results to clients is what the WebSocket is for and it needs no pool of pending responses.
 - A read has to reply with data, so it does wait, without blocking: its chunked response sends nothing until `loop()` has filled the read's ModelSnapshot.