feat: configure footer version links

[JOY (JOY)]

Summary

• add runtime repository and release link configuration for footer versions
• preserve upstream Blockscout defaults
• document the variables in README and ENVS
• sync README to the Docker Hub description during image publishing

Validation

• 4 focused unit tests pass
• TypeScript check passes
• changed-file ESLint and cspell pass
• env validator passes with the generated registry and test preset
• independent review completed with no remaining must-fix findings

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.