docs: correct multi-bot FAQ and make GHCR primary in Images table

[libre-7]

Correctness leftovers from the 2026-08-23 review:

• Multi-bot FAQ: previous answer ("use separate data directories and ports") was false — port 5225 is hardcoded in entrypoint.sh, Dockerfile EXPOSE, healthcheck.py, and first-run setup. Replaced with an accurate answer (separate containers/network namespaces; SIMPLEX_SOCAT_PORT note with unauthenticated-mode warning).
• Images table: reordered so GitHub Container Registry is listed as primary, matching the Quick Start registry ordering.

Docs-only change. Finding A (dead nc fallback) was already resolved on main via #17 — verified no nc/netcat references remain in entrypoint.sh/Dockerfile.