Add supports_progress_text_metadata feature flag and extend
send_progress_text() to accept optional prompt_id param. When
prompt_id is provided and the client supports the new format,
the binary wire format includes a length-prefixed prompt_id field:
[4B event_type][4B prompt_id_len][prompt_id][4B node_id_len][node_id][text]
Legacy format preserved for clients without the flag.
Both callers (nodes_images.py, client.py) updated to pass prompt_id
from get_executing_context().
Part of COM-12671: parallel workflow execution support.
Amp-Thread-ID: https://ampcode.com/threads/T-019c79f7-f19b-70d9-b662-0687cc206282
1c7e656eb4