upgrade docker image, fix readme, remove deprecated gem-install flags

[laur89]

Pre-flight Checklist

Please ensure you've completed all of the following.

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.

Description of Change

• update references to Ferdium 6 -> 7 throughout the documentation/code
• upgrade Dockerfile baseimage to Bookworm (current Debian stable)
• remove deprecated gem install options --no-ri & --no-rdoc that cause installation to fail
• add architecture detection to pnpm build in Dockerfile

Motivation and Context

Main importance are the Dockerfile baseimage upgrade as currently used image is no longer available. This in turn pulls in newer ruby/gem which causes gem install statements to fail due to abovementioned deprecated options.

Basically this change re-enables the ability to build ferdium via provided Dockerfile.

Checklist

• My pull request is properly named
• The changes respect the code style of the project (pnpm prepare-code)
• pnpm test passes
• I tested/previewed my changes locally

Release Notes

none

[vraravam]

@all-contributors please add @laur89 for code

[allcontributors]

@vraravam

I've put up a pull request to add @laur89! 🎉