migration: remove Forgejo dependencies

[thedancingdeveloper]

Summary

• switch all librtbit dependencies from the Forgejo Cargo registry to pinned GitHub sources
• remove Forgejo Cargo credentials/configuration from CI and Docker builds
• point metadata and deployment documentation at the canonical TheDancingDeveloper-org image/repository

Validation

• cargo fmt --all -- --check
• cargo check --workspace --all-targets --locked
• cargo test --workspace --locked
• cargo test --workspace --doc --locked
• cargo clippy --workspace --all-targets --locked -- -D warnings

This is the migration cutover for the indexarr-rs source and build path; runtime pins will be advanced after the protected branch checks pass.