docs: link to live repository tree

[CleanDev-Fix]

Summary

• replace the stale five-entry file tree with a link to the live repository listing
• keep the file-structure guidance accurate as tests, docs, workflows, and tooling evolve

Changes

• update the File Structure section in vesting.md only
• remove the incomplete static tree without changing contract or test behavior

Testing / Verification

• confirmed the live repository link returns HTTP 200
• confirmed the issue-cited paths exist in the current repository tree
• confirmed the stale diagram is absent and Markdown fences remain balanced
• ran git diff --check

Fixes #356