Add Package References to Compiler

[agocke]

Priority: P0
Estimate: 2-3 hours
Status: Not Started
Depends on: Task 4.1 - Read project.assets.json in BuildCommand

Description

Extract package compile assemblies from lock file and add them to compiler references.

Tasks

• [ ] Extract package compile assemblies from lock file
• [ ] Add package assemblies to Csc.References
• [ ] Handle reference conflicts (prefer package over framework)
• [ ] Add proper error messages for missing packages

Files to modify

• src/Dn/BuildCommand.cs

Acceptance criteria

• Projects with PackageReferences build successfully
• Compiler sees both framework and package references
• Clear error if restore needed but not run

Phase

🔴 CRITICAL - Phase 4: Complete Restore Integration