fix(terminal): stop heartbeat pong leaking into the PTY as input

The WebSocket control-frame heuristic only recognized resize/ack/reset,
so the frontend's heartbeat reply {"type":"pong"} fell through to
write_input() and was typed into the shell / pi every ~30s. That garbage
corrupted the foreground app: stray text in the input line, rerenders,
and scroll-position resets (visible on resize/scroll redraws).

Treat any text frame that parses to a JSON object carrying a "type" field
as control traffic that must NEVER reach the PTY: handle known types and
ignore unknown ones. Keystrokes, bracketed-paste content, and plain text
are still forwarded as raw input.

apps/api/src/api/system/terminal.py

@@ -334,22 +334,20 @@ async def _write_loop(session_ref: SessionRef, websocket, instance_id: str) -> N
                     await session.write_input(message["bytes"])
                 elif "text" in message:
                     text = message["text"]
-                    # Treat a text frame as a control message only when it
-                    # is a JSON object carrying a known "type". Anything
-                    # else — including JSON-shaped pastes — is forwarded as
-                    # raw terminal input so multiline and bracketed-paste
-                    # content is never silently swallowed or misrouted.
+                    # A text frame that parses to a JSON object with a
+                    # "type" field is a control message and must NEVER be
+                    # written to the PTY (e.g. the heartbeat {"type":"pong"}
+                    # must be consumed, not typed into the shell/pi). Handle
+                    # known types and ignore unknown ones. Everything else
+                    # (keystrokes, bracketed-paste content, plain text) is
+                    # forwarded as raw terminal input.
                     ctrl = None
                     if text.startswith("{"):
                         try:
                             parsed = json.loads(text)
                         except json.JSONDecodeError:
                             parsed = None
-                        if isinstance(parsed, dict) and parsed.get("type") in (
-                            "resize",
-                            "ack",
-                            "reset",
-                        ):
+                        if isinstance(parsed, dict) and "type" in parsed:
                             ctrl = parsed
 
                     if ctrl is None: