Fixes#1552
OpenAI's structured outputs API requires all properties to be in the
'required' array of JSON Schema. Zod's .default() makes fields optional,
causing codex-cli provider to fail with 'Missing dependencies' error.
Changes:
- Removed .default() from SubtaskSchema, BaseTaskSchema, UpdatedTaskSchema
- Added application-level default handling in expand-task, update-task-by-id,
update-tasks, and parse-prd-streaming
- Ensures all schema properties are marked as required for OpenAI compatibility
- Maintains backward compatibility by applying defaults when AI doesn't provide values
Co-authored-by: Ralph Khreish <Crunchyman-ralph@users.noreply.github.com>
