chore(funding): placeholder funding template

[hkimw]

Summary

• Add a comment-only FUNDING.yml placeholder
• Document how to enable approved funding providers later
• Keep all funding entries inactive with no actual funding URLs

Tests

• Not run (documentation-only change)

[hkimw]

This PR is now superseded by #27, which has been merged to main with a placeholder FUNDING.yml that explicitly cross-references the canonical sponsorship policy at `pccxai/pccx/docs/commercial/sponsorship-policy.md`. The two PRs cover the same intent (comment-only FUNDING.yml, no active sponsor URL). Recommending close as superseded; reopen only if a different placeholder design is preferred.

Both PRs preserve the safety posture: no verified GitHub Sponsors handle, no fake URL, sponsorship is acknowledgement-only and not investment.