feat(cli): add --output-schema flag - #17276

Issue for this PR

Closes #9320
Closes #10456

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This PR extends the output schema SDK feature added in a previous PR to the opencode run cli.
This adds the flags --output-schema to allow defining the json-schema contents
The value for --output-schema can be either a json compatible string or a path to a file containing a json compatible string.

How did you verify your code works?

$ bun run dev run -- "hello world" --output-schema "{\"type\":\"object\",\"properties\":{\"is_hello_world\":{\"type\":\"boolean\"}},\"required\":[\"is_hello_world\"]}"
{"is_hello_world":true}

Screenshots / recordings

If this is a UI change, please include a screenshot or recording.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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