[FEATURE]: support JSON schema as a constrain of opencode run command

[richardanaya]

Feature hasn't been suggested before.

• [x] I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Support for new --json on opencode run command similar to llama.cpp cli

''' opencode run -m opencode/grok-code --json '{"type":"object","properties":{"colors":{"type":"array","items":{"type":"string"}}},"required":["colors"]}' "make 3 colors" '''