Adds a Canvas LMS integration skill under optional-skills/productivity/canvas/
with a Python CLI wrapper (canvas_api.py) for listing courses and assignments
via personal access token auth.
Cherry-picked from PR #1250 by Alicorn-Max-S with:
- Moved from skills/ to optional-skills/ (niche educational integration)
- Fixed hardcoded ~/.hermes/ path to use $HERMES_HOME
- Removed Canvas env vars from .env.example (optional skill)
- Cleaned stale 'mini-swe-agent backend' reference from .env.example header
Co-authored-by: Alicorn-Max-S <Alicorn-Max-S@users.noreply.github.com>
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