Add project ledger poem

[justusaugust]

Summary

• Add POEM.md with an original four-stanza poem written for the FreelanceFlow project
• Add demos/project-ledger-poem-demo.mp4 as a short proof video for the submitted poem

Creative note

I used a ledger-and-light motif because the project is about trust, milestones, payment flow, and clear records between clients and freelancers.

Validation

• Confirmed POEM.md has four stanzas
• ffprobe demo inspection: 1280x720, 6s MP4
• git diff --check

/claim #76