Single-source dependency declarations through the DSL

[JPDuchesne]

Summary

• The declarations list is now the single data model for dependencies: GroupDSL/EnvDSL no longer dual-write into @brew/@envs shadow hashes, and Config#group is gone. bin/install-build-deps.rb derives the container image's install list by filtering config.declarations (integration == :brew, group == :build, env/host filters mirroring DependencyInstaller).
• Env-scoped brew now peels post_install and host: onto the declaration exactly like group-level verbs do (previously they leaked into the constraint hash on the env path).
• All dependency verbs (shared DependencyVerbs module) now work at the top level of Dev::Deps.define, landing in the default :app group — the same convention a top-level gem always followed.
• README documents the dev-owned group vocabulary (:app runtime default, :development/:test, :build toolchain materialized into build images, domain groups) and drops the dual-write description.

Verification

• Full suite: 937 tests, 0 failures; rubocop clean.
• Diffed the build-image collection (taps, install specs, cask/version/tap handling, host-gated skips, post_install ordering) old code vs new against cellbound-3d's real manifest: byte-identical. cellbound's manifest is stale (uses the long-removed ruby_version verb) and fails identically under both.

Made with Cursor

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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