docs: document Garage instead of MinIO as the object store

[PhilippTheServer]

Closes #15

Companion to OpenTaberna/fastapi#60. Merge after that one, since these pages describe its dev stack.

• Getting-Started: the opentaberna-garage service and ports, plus the GARAGE_RPC_SECRET step after cp .env.example .env.
• Configuration: the object storage section explains Garage's key and region setup.
• Deployment, home, API/Architecture, Orders-and-Fulfillment: production is described as "an S3-compatible object store (Garage, Ceph RGW or AWS S3)", and the backup advice uses rclone sync instead of mc mirror.
• date front matter bumped on every edited page.

Verification

$ python3 tools/check_wiki.py
Checked 8 pages against 43 API paths.
OK — every endpoint is documented, and every documented path exists.
$ grep -rni minio . --exclude-dir=.git | grep -v openapi.snapshot | wc -l
0

The setup one-liner, run against a sample .env, filled in a 64-hex-character secret and left no .bak file behind.

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