oxlog does not find archived live log files

#9226 added archival of live log files from zones when they shut down and when the sled reboots. But they get named slightly differently and oxlog doesn't find them. After a recent dogfood update:

BRM27230045 # ls -1 /pool/ext/*/crypt/debug/*nexus_dcb*/*nexus* > all_logs.txt

BRM27230045 # /opt/oxide/oxlog/oxlog logs oxz_nexus_dcb27edf-5a97-459a-92c0-63d795744055 nexus --archived > oxlog_logs.txt

BRM27230045 # diff oxlog_logs.txt all_logs.txt 
137a138,139
> /pool/ext/8a0016f3-3cdc-4b4c-b1d3-5334dd365465/crypt/debug/oxz_nexus_dcb27edf-5a97-459a-92c0-63d795744055/oxide-nexus:default.1761086667
> /pool/ext/8a0016f3-3cdc-4b4c-b1d3-5334dd365465/crypt/debug/oxz_nexus_dcb27edf-5a97-459a-92c0-63d795744055/oxide-nexus:default.1761098396

There are two choices here:

• teach oxlog about these paths. (pro: will cover files already archived with this problem. risk: is there some other file in these datasets that it will mistakenly pick up?)
• change sled agent to preserve the .log in this case. This seems better, but would require more testing (this code is not factored in a way that makes it testable without fully running it all, including archiving on a deployed system) and oxlog would never pick up log files that had been archived without this fix.

Start with the oxlog logs command and the archived path patterns shown in the issue, then compare them with the sled agent archival behavior introduced by #9226. Decide whether oxlog should recognize the existing filenames or sled agent should preserve the .log suffix; done means archived live logs are found without unrelated files being included, with testing covering the chosen behavior.