fix(channels): include message id in /api/messages response

/api/messages was dropping channel_messages.id when building the response
dict. The frontend therefore had msg.id=undefined for history-loaded rows,
so createMessageElement's "typeof msg.id === 'number'" guard suppressed
the raw-resend button, and refreshMessagesMeta couldn't find the wrappers
either (data-msg-id only gets set when msg.id is truthy). End result: the
raw-resend button only appeared on messages sent in the current session
and was lost on every channel switch or page reload.

Surfacing id costs nothing — the field already exists on the row — and
also unblocks any future per-message UI that needs to address the row
directly. createMessageElement already handles undefined id correctly for
older clients, so this is a one-way frontend benefit.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/routes/api.py

@@ -470,6 +470,7 @@ def get_messages():
                     hop_count, path_hash_size, _ = decode_path_len(path_len_raw)
 
                 msg = {
+                    'id': row.get('id'),
                     'sender': row.get('sender', ''),
                     'content': row.get('content', ''),
                     'timestamp': row.get('timestamp', 0),