chore(build): add opt-in development feature bundles - #5005

Summary

Add an opt-in dev Cargo feature bundle for the gateway and supervisor. Normal development builds and tests enable it; prerelease and stable builds leave it disabled.

Related Issue

Build configuration for #4411. The Cedar implementation is stacked above this branch in #5006.

Changes

• Enable dev in existing workspace build, check, lint, and test commands.
• Add a dev-build boolean to binary builds; Release Dev and branch E2E builds opt in.
• Document the development configuration without adding CI jobs or additional test passes.

Release Notes

Testing

• Workflow lint, YAML/TOML parsing, and Markdown checks passed.
• Cargo feature resolution verified with and without dev.
• Repository pre-commit checks, including workspace Clippy with --features dev, passed.

Checklist

• Follows Conventional Commits.
• Commits are signed off (DCO).