fix: resolve local types from dependency packages

[nook4sh]

What changed

• Preserve package path context when parsing type definitions from external dependency files.
• Avoid panics when resolving package paths for files that were not collected through the normal search-dir path.
• Add a minimal regression fixture where a dependency package type references another type from the same package using an unqualified identifier.

Why

When a dependency type is parsed from an external package and its fields reference sibling types without a package qualifier, swag can lose the file-to-package-path context and fail with errors such as cannot find type definition.

Tests

• go test ./ -run 'TestPackagesDefinitions_FindTypeSpecFromExternalPackageFile|TestParseDependencyLocalTypeInNonUniquePackage' -count=1
• go test ./...