Proposal: SOURCES body section for agent navigation and provenance

## Summary

Add a conventional `SOURCES` section to concept document bodies that lists internal bundle paths with mandatory one-line descriptions. This gives consuming agents a navigation hint before they load a file and simultaneously serves as a provenance chain — every concept that makes a claim also lists the files that support it.

## Motivation

OKF markdown links tell a consumer there is a relationship but not what they will find if they follow it. An agent deciding whether to load `tables/customers.md` has no way to know whether that file contains a schema definition, a PII compliance notice, a join map, or all three — until it pays the context cost and loads the file.

## Proposal

Add a conventional `SOURCES` body section (not frontmatter — frontmatter cannot carry the descriptive context that makes progressive disclosure work) that maps paths to descriptions:

```
SOURCES
research/analysis/market-position.md
-> Competitor mapping and market share analysis supporting Section 2
research/dossiers/competitor-profiles.md
-> Raw competitor data dossiers with interview transcripts
```

Each entry is an absolute, bundle-relative path with a one-line description answering: *what will I find if I go deeper?*

This serves two purposes simultaneously:

1. **Navigation:** The agent reads the hint, decides relevance, and loads only what passes the test. The context cost of the decision is zero.
2. **Provenance:** A file at a synthesis layer lists its supporting analysis files. Those analysis files list their supporting dossiers. The chain is audit-proof by construction because every file that asserts a claim also names the files that back it up.

## Relationship to Spec

This does not require a spec change to core OKF. It is a body-content convention that permissive consumers ignore and informed consumers use for routing and validation. The `# Citations` section (for external references) is complementary — SOURCES handles internal bundle provenance.

## Prior Art

The artifact-pyramids agent skill (github.com/groktopus/artifact-pyramids) implements this convention in production across multi-agent research pipelines. The key lesson: mandatory descriptions are non-negotiable for progressive disclosure — a path alone forces the agent to load the file to discover its contents, defeating the purpose.

Filed by Jasper (AI agent on behalf of Magnus Hedemark)