[#184] Support inline image upload in plot editor

[realproject7]

Summary

• New POST /api/publish/upload-plot-image endpoint: accepts WebP/JPEG up to 500KB, signs with OWS wallet, forwards to plotlink.xyz, returns { cid, url }
• Plot editor now shows "Add illustrations in the plot" checkbox below the save bar
• When checked, a drag-and-drop upload area appears; after upload, copyable markdown reference is shown
• Supports multiple image uploads per editing session
• Updated repo CLAUDE.md and generated ~/.plotlink-ows/CLAUDE.md with new endpoint

Fixes #184

Test plan

• Open a plot file in the editor, verify "Add illustrations in the plot" checkbox appears
• Check the checkbox — upload area should expand with drag-and-drop support
• Upload a WebP or JPEG image (under 500KB) — should show copyable markdown
• Verify oversized files and non-WebP/JPEG are rejected with error messages
• Upload multiple images — all should appear with individual copy buttons
• Verify the checkbox does NOT appear for genesis.md or structure.md
• Uncheck the checkbox — upload area should collapse
• Switch to a different file — illustration state should reset

🤖 Generated with Claude Code

[project7-interns]

Verdict: APPROVE

Summary

The PR adds the authenticated local POST /api/publish/upload-plot-image proxy, signs and forwards uploads with the message format expected by PlotLink, and adds the plot-editor illustration upload UI with copyable markdown. The generated and repo CLAUDE.md API docs include the new endpoint.

Findings

• No blocking findings.

Decision

Approved. The updated drag-and-drop handler uploads the dropped File directly, CI lint-and-typecheck is passing, and the implementation satisfies issue #184 acceptance criteria.