Fix trailing slash, response leak, NPE, and minor issues in module system

[pditommaso]

Summary

Stacked on #6929. Fixes 8 additional issues found during code review:

Important fixes:

• Trailing slash in registry URLs causes 404s -- RegistryConfig now strips trailing slashes from configured URLs, preventing double-slash paths like https://registry.../api//v1/modules/
• HTTP response body InputStream not closed -- ModuleRegistryClient.downloadModule() now wraps response.body() in try-with-resources after Files.copy() to avoid leaking connections
• NPE when release.metadata is null -- CmdModuleInfo logged a warning but continued to access metadata.description, causing NPE. Now throws AbortOperationException instead
• Inconsistent ModuleInfo.load() return types -- load(Path) returned [:] while load(Path, String) returned null for missing files. Now both return null consistently

Minor fixes:

• Duplicate isRemoteModule regex -- Extracted pattern to ModuleResolver.REMOTE_MODULE_PATTERN constant; added cross-reference comment in ModuleReference to keep them in sync
• removeModule returns null instead of false -- Bare return in a boolean method now explicitly returns false
• Typo in error message -- "No module diretory" fixed to "No module directory" in CmdModulePublish
• Unclosed Files.walk() stream -- ModuleStorageTest.createTestPackage() now closes the stream via withCloseable{}

Test plan

• ModuleInfoTest passes (updated to expect null instead of [:])
• ModuleStorageTest passes
• CmdModuleInfoTest passes
• CmdModulePublishTest passes
• ModuleReferenceTest passes
• Full compilation succeeds