docs(cli): document agent / CI usage for deno deploy and deno sandbox

Adds a dedicated 'Agent / CI usage' section to the deno deploy CLI
reference covering the conventions that make non-interactive use
reliable: token discovery order, the global --json / --non-interactive /
--quiet / --debug / --token / --endpoint / --config flags, exit-code
taxonomy (0/1/2/3/4/5/6), the structured error envelope on stderr in
--json mode, the per-subcommand JSON output schemas, the
non-interactive flag coverage table, stdio discipline, and copy-pasteable
examples.

Also fills out the previously incomplete 'Global options' (most global
flags were undocumented) and splits root-command options from globals.
Cross-links the same conventions from the deno sandbox CLI reference.

Author: crowlbot