`reparentWorkspaceTreeRoot` was unconditionally wrapping every primary
workspace module's tree root with a synthetic parent named after the
module, so every check/generator/service path was rendered as
`<module>:<item>` — including the workspace's own root module.

As a result, `dagger check -l` on this repo showed
`dagger-dev:generated` instead of just `generated`, contradicting the
documented behavior (docs/current_docs/introduction/core-concepts/checks.mdx)
where only toolchain items are namespaced. The integration contract is
already asserted strictly for toolchains by `TestChecksAsToolchain` but
only loosely for main modules by `TestChecksDirectSDK` /
`TestChecksAsBlueprint` (via `Contains`, which accepts either form).

Fix: have `SchemaBuilder.PrimaryMods` also return the set of "main"
(entrypoint-proxied) module names, and skip the reparent for those
modules inside `reparentWorkspaceTreeRoot`. Main modules are the ones
installed with `Entrypoint` — the workspace root module or a blueprint —
whose main-object methods are proxied onto the Query root. Toolchain
modules remain prefixed with their module name.

Also strengthen `TestChecksDirectSDK` and `TestChecksAsBlueprint` with
`NotContains` assertions on the prefixed form, so a future regression
surfaces immediately.

Signed-off-by: Yves Brissaud <yves@dagger.io>