Add source workspace discovery and evidence inventory for package compilation

## Problem statement Before Lineage can compile a workflow, it needs a deterministic inventory of the source workspace. Today package discovery starts from `lineage.yaml`; this new path must inspect existing agent-workflow folders that may not already be valid Lineage packages. ## Scope - Add a read-only discovery pass for source workspaces. - Inventory agent instruction files such as `CLAUDE.md`, `AGENTS.md`, and nested `SKILL.md`/`WORKFLOW.md` files. - Inventory scripts, prompts, reference files, setup notes, and existing package manifests when present. - Classify each artifact as instruction, executable helper, reference, setup material, package metadata, or unknown. - Record file paths, content digests, size, language/type, and why each artifact was included. ## Acceptance criteria - Discovery runs without creating, editing, deleting, or executing source files. - Output is deterministic for the same source tree. - Ignored directories such as `.git`, dependency folders, generated archives, and common build output are skipped by default. - Tests cover mixed Claude/Codex workspaces, nested skills, scripts, references, and ignored paths. - The inventory can be serialized for the later behavioral-model issue. ## Dependencies - Should reuse existing package safe-path assumptions from #31 and related validation work. ## Non-goals - No agent/LLM analysis in this issue. - No package artifact generation in this issue. - No execution of discovered scripts. ## Sequencing First child issue in the workflow-understanding milestone. The behavioral model and Claude-assisted analysis issues consume this inventory.