Normalize program names in shellparse.Parse to their basename.
Does not rely on filepath.Base because the server may run on either
Linux or Windows where the behavior would differ.
Closes CODAGT-470
When the execute tool runs a chained shell command, the UI previously
rendered the raw string. Long chains like "cd /repo && git pull &&
git add . && git commit -m fix" were hard to scan.
A new ChatMessagePart.ParsedCommands [][]string field on tool-call
parts carries one entry per simple command, parsed in chatd from args
via mvdan.cc/sh/v3/syntax. The frontend renders the joined list ("cd,
git pull, git add, git commit") in place of the raw command, and falls
back to the raw command when the field is absent.
Closes CODAGT-446
Mathias Fredriksson