- Add `add_comment_as_user()` to PaperclipClient using a second httpx
  client keyed with PAPERCLIP_FOUNDER_USER_API_KEY; falls back to agent
  key with a warning when env var is absent
- Switch /comment and forward_to_inbox in bot.py to call
  `add_comment_as_user` so comments are recorded as authorUserId, not
  authorAgentId
- Add two new tests for the new method (user-key path + fallback)
- Update existing bot tests to expect `add_comment_as_user`
- Document PAPERCLIP_FOUNDER_USER_API_KEY in README

Co-Authored-By: Paperclip <noreply@paperclip.ing>