[Foundation] FT-5: Context-scope tool-path resolvers and process defaults

[ChrisonSimtian]

Summary

Move tool-path resolver configuration and process defaults onto BuildContext (keeping static facades), so the engine stops writing process-global statics mid-run.

Findings (file:line)

• BuildManager.cs:53-56 writes NuGetToolPathResolver.{EmbeddedPackagesDirectory,NuGetPackagesConfigFile,NuGetAssetsConfigFile} and NpmToolPathResolver.NpmPackageJsonFile — mutable public statics, never reset.
• ProcessTasks.DefaultLogOutput / DefaultLogInvocation / DefaultWorkingDirectory — mutable global defaults.

Scope

• Hold tool-path + process defaults on BuildContext.Tools.
• Resolvers read from the context; keep static facades for backwards compatibility.
• Remove the direct static writes from BuildManager.Execute.

Acceptance criteria

• BuildManager.cs:53-56 no longer assigns process statics; resolution reads from ctx.
• Tool resolution behavior unchanged for normal runs.

Notes

• Non-breaking (facades preserved).
• Depends on: FT-2.
• Size: M.