Fix Reddit comment API payload

[iloveyamlfries]

Summary

• send comments to /api/comment with Reddit's expected api_type=json, thing_id, and text payload
• raise on Reddit json.errors responses so failed comments do not print false success
• make unresolved cached indexes fail with a nonzero Click error instead of returning silently

Verification

• .venv/bin/python -m pytest
• .venv/bin/python -m ruff check .

Manual validation

• Compared the CLI payload with a Chrome DevTools capture of Reddit's /api/comment request shape
• Verified a real public rdt comment call succeeds after the fix