Save a new instructions version

Appends a version and makes it active. Token callers create a `teach` version - use after a reviewer sends a draft back with feedback: rewrite the instructions with your own AI step, then save the result here with the reviewer's comment and the output it came from. Dashboard sessions create `manual` edits or restores.

curl -X POST "https://example.com/api/instructions/versions" \  -H "Content-Type: application/json" \  -d '{    "project": "string",    "task": "string",    "content": "string"  }'

{  "version": 0}