Rojo resolver

[AlternativeLua]

• RojoProject / RojoNode — parse default.project.json.
• RojoResolver — walk the tree, resolve $paths relative to the project dir, and locate loom_runtime.luau → instance-path segments.
• RuntimeImport + CompilationUnit — three-way resolution (Resolved / RojoMissing / NotFoundInRojo) with the single-source default path.
• LuauGenerator — emits require(...) at the resolved path, warns (L353) on a misconfigured Rojo project, and stays silent + defaulted when there's no Rojo file.
• Tests — resolver algorithm + wiring + end-to-end,

Test Usage

dotnet run --project ../Loom.CLI --
rojo build default.project.json -o demo.rbxlx
rojo serve default.project.json

Closes issue #21