Use direct HTTP API for IPFS instead of ipfshttpclient

Replace ipfshttpclient library with direct HTTP requests to IPFS API.
This fixes compatibility with newer Kubo versions (0.39.0+) which are
not supported by the outdated ipfshttpclient library.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

requirements.txt

@@ -7,4 +7,3 @@ python-jose[cryptography]>=3.3.0
 markdown>=3.5.0
 python-multipart>=0.0.6
 asyncpg>=0.29.0
-ipfshttpclient>=0.7.0