fix: track what a primary module interface imports

A primary module interface unit — `export module Widget;`, no partitions —
recorded nothing about what it imported. GetInterfacesAndImplementations
registered the Module and then erased the file from the scan list, so the
import pass only ever saw partitions, and Module had no vectors to hold an
edge anyway.

Two consequences, both reported as issue #26:

  Module::Check consulted only its own .cppm and its partitions. A data
  member added to an imported module left Widget.pcm, Widget.o and every
  consumer object untouched while the imported library rebuilt and both
  binaries relinked — one executable holding two class layouts, no
  diagnostic, and a crash somewhere unrelated. Wiping build/ was the only
  cure, so `crafter-build test` could not be trusted straight after an
  interface edit.

  Module::Compile waited on nothing. Two modules in one Configuration
  compile on concurrent threads, so a primary interface importing a
  sibling was a coin flip between working and "module 'Base' not found".

Partitions never had either problem — they carry the same three vectors and
Check/Compile honour them — which is why the gap only surfaced on a module
whose interface is one flat unit.

Module now carries moduleDependencies, externalModuleDependencies and
pendingImports with the same meanings as on ModulePartition; primary units
stay in the scan list so their imports land there; Check sees through them;
Compile orders itself behind a local sibling; and ResolvePendingImports
sweeps them so an edge survives dependencies being wired up afterwards.
Build() now Checks every interface before spawning any compile thread — the
`compiled` flag a waiter blocks on is raised either by a Compile that runs
or by the Check that decides none is needed, so a Check still pending while
another module's thread waits would have hung the build.

Resolves #26

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

project.cpp

@@ -108,6 +108,7 @@ extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> a
         cfg.AddTest("ModuleInterface").Dependencies({ CrafterBuildLib.get() });
         cfg.AddTest("DependencyLink").Dependencies({ CrafterBuildLib.get() });
         cfg.AddTest("IncrementalInterfaceChange").Dependencies({ CrafterBuildLib.get() });
+        cfg.AddTest("TransitiveInterfaceChange").Dependencies({ CrafterBuildLib.get() });
         cfg.AddTest("CleanProject").Dependencies({ CrafterBuildLib.get() });
         cfg.AddTest("ShaderCompile").Dependencies({ CrafterBuildLib.get() });
         cfg.AddTest("StandardArgs").Dependencies({ CrafterBuildLib.get() });