Remove or convert stale issue proposal document #30
Description
Priority: P2 | Source: PR #21 self-review (F6)
Problem
.github/ISSUE_PROPOSAL_mechanical_diagrams.md describes 5 separate PRs, but PR #21 implemented all 5 in a single PR. The proposal is a stale planning artifact on merge.
Suggested Fix
Either convert to a GitHub Issue (which can be closed when done) or remove the file since it has served its planning purpose. Stale planning docs checked into the repo create confusion for future readers.