Compile provider-neutral package artifacts from the behavioral model

## Problem statement The first artifact generator should create the provider-neutral package structure. Provider-specific files can only be correct if the shared package manifest, workflows, skills, references, capabilities, and setup declarations are already coherent. ## Scope - Generate `lineage.yaml` from behavioral-model metadata. - Generate `workflows//WORKFLOW.md` with ordered steps compatible with #49. - Generate `skills//SKILL.md` files for deterministic and agent-mediated steps. - Generate references and setup metadata declared by the model. - Preserve evidence comments or metadata where useful for review. ## Acceptance criteria - Generated packages pass `lineage package validate` from #31. - Workflow steps reference generated or required skills correctly. - Package generation is deterministic for the same behavioral model. - Tests cover a simple workflow, a multi-step workflow, references, and required external skills. - The generator does not emit provider-specific instructions except through later provider emitters. ## Dependencies - Depends on the behavioral model from the previous milestone. - Builds on the workflow model used by #49. ## Non-goals - No Claude-specific or Codex-specific context generation in this issue. - No sanitization pass beyond producing structurally valid package files. - No registry publish or pull changes. ## Sequencing First child issue in artifact compilation. Provider-specific emitters should build on this package output.