chore: drop sops+age

[cmdoret]

As this repo only takes care of publishing helm chart, it does not need the secret management stack.

[Copilot]

Pull request overview

This PR removes the repository’s SOPS+age-based secret-management tooling and related documentation/configuration, aligning the repo with its stated purpose of publishing a Helm chart rather than managing encrypted deployment secrets.

Changes:

• Removed SOPS/age from the Nix dev shell toolset and deleted SOPS-related Just module/config files.
• Simplified just deploy to use the provided values file directly (no decryption step).
• Removed/updated documentation and examples that referenced encrypted secrets and SOPS setup.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tools/nix/flake.nix	Drops age/sops from dev shell tools.
tools/just/sops.just	Removes the SOPS Just module entirely.
tools/config/sops.yaml	Removes SOPS encryption rules and age recipients from the repo.
tools/config/gitleaks_extend.toml	Removes SOPS-specific gitleaks extension rules.
README.md	Removes Secrets section referencing SOPS+age flow.
justfile	Removes sops module; deploy/check-leaks simplified.
example.env	Removes SOPS key env var example.
docs/CONTRIBUTING.md	Removes Secrets section; updates examples of specialized just recipes.

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