Consolidate the CLI output/error contract so agents can predict behavior
from a command's declaration:
- --json / --format resolved through a single FormatCapabilities set;
explicit --format wins over --json across api, service, shortcut and
auth scopes
- --format pretty renders as indented JSON via its own Format case,
no longer aliased to table
- a single root FlagErrorFunc classifies pflag typed errors; the mail
and sheets local FlagErrorFunc hooks are removed
- cobra argument, required-flag and flag-group errors are typed at their
validation stage; the usage-error text markers are removed
- root and group unknown commands return structured suggestions
- manifest-export marks pure group nodes as non-runnable
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