linkTaskManagerChoice: guard calling methods on None
linkTaskManager: Log error location, input
ChoicesDict: implement .fromstring constructor
Revert "linkTaskManagerChoice: print backtraces"

Stderr is already being printed into the MCPServer log, and the
Dashboard log is owned by a different user so this introduced unexepcted
issues.

It would still be advantageous to convert the MCPServer to use the
logging module in the future.

This reverts commit 94d9c36ec3a4ac47baf28ae588d3863cc4389d3f.