fix(spin-common,spin-java-module): enforce cross-project compile ordering from module graph

[deer]

Invocable.dependencies() hardcoded getProject() on every @From reference, so the task graph contained no cross-project edges at all. The parallel scheduler could — and did — run A.DetectCompilationResolution before B.Compile finished, caching a module path that omitted B entirely. PR #63 turned a pre-existing race condition into a guaranteed failure: before it, the non-existent sibling output path was always added to candidates and javac would silently skip it; after it, Optional.empty() from resolveFallbackOutput dropped the sibling completely.

• Adds Plugin.projectDependencies(forTaskClass) — a new extension point in spin-api that lets plugins declare cross-project task dependencies. Default implementation returns an empty stream so existing plugins are unaffected.
• Overrides DefaultInvocable.dependencies() in spin-common to concatenate intra-project @From dependencies with plugin.projectDependencies(taskClass), feeding cross-project references into the existing scheduler machinery with no changes to DefaultProgram.
• Implements projectDependencies in AbstractJavaPlugin: when the task being scheduled is an AbstractDetectResolution subclass (main or test), reads the plugin's module descriptor, finds workspace siblings that own any of the required module names, and returns those siblings' Compile task references as ordering constraints.