The bundled extension is ship, and it lives under druks.contrib

[czpython]

build was the platform's only package that was really an app: druks/build sat beside druks/durable and druks/events as if it were platform. It moves to druks/contrib/ship, so the import path says which layer a module belongs to, and the extension takes the name the product uses.

• druks.build → druks.contrib.ship; extension class Build → Ship, name = "ship"; entry point ship = "druks.contrib.ship.extension:Ship".
• The BuildWorkflow class becomes Build — inside the app it is still a build — so its durable kind is ship.build and the profiler's is ship.profile. BuildWorkspace, BuildJournal, BuildPromptContext hang off that workflow and keep their names.
• Prompts move to templates/prompts/ship/, with build_workflow/ flattened to build/; names are ship/build/*.md, so a repo override lives at .druks/ship/prompts/build/*.md.
• Frontend routes and API namespace move from /build to /ship.
• The loader-purity test now guards the whole druks.contrib namespace instead of one extension.
• One revision rewrites what is already in Postgres: settings_overrides.key extension:build: → extension:ship:, and durable_runs.kind build.% → ship.%.

Verified: ruff check, ruff format --check, pyright (135 errors, unchanged from main), pytest --collect-only (959 collected), frontend vitest (51 passed).