[Docs] Fix CONTRIBUTING.md correctness: malformed front-matter, wrong GitHub org URLs, wrong Postgres port

[grantfox-oss]

Telegram (ask questions / claim the issue here first): https://t.me/+DOylgFv1jyJlNzM0

Why this matters

CONTRIBUTING.md has a malformed YAML front-matter block (a --- at line 1 with the # Contributing to FlowFi H1 inside it and the closing --- at line 9) that GitHub renders incorrectly; lines 15-17 link to github.com/flowfi/flowfi although the repo lives at LabsCrypt/flowfi; and line 109 states PostgreSQL (port 5432) while docker-compose.yml maps host port 5433.

Acceptance criteria

• Remove the stray --- front-matter wrapper so the H1 renders as a normal heading
• Change flowfi/flowfi URLs to LabsCrypt/flowfi
• Correct the Postgres port to 5433 to match docker-compose.yml

Files to touch

• CONTRIBUTING.md
• docker-compose.yml

Out of scope

• README.md (already corrected)