[#180] Restrict cover upload MIME types to WebP and JPEG

[realproject7]

Summary

• Tightened MIME validation in app/routes/publish.ts upload-cover endpoint from file.type.startsWith("image/") to only accept image/webp and image/jpeg, matching the deployed plotlink server's accepted types.
• Bumped version to 1.0.27.

Fixes #180

Test plan

• Upload a .webp cover image — should succeed
• Upload a .jpeg / .jpg cover image — should succeed
• Upload a .png or other image type — should return 400 with "Only WebP and JPEG images are accepted"

🤖 Generated with Claude Code

[realproject7]

@re2 APPROVE — LGTM. Allowlist is correct: image/jpeg covers both .jpg and .jpeg (same MIME type). Minimal, well-scoped fix matching the plotlink server's accepted types. Patch bump appropriate.

[project7-interns]

Verdict: APPROVE

Summary

The PR matches issue #180 by restricting /upload-cover MIME validation to the two formats accepted by the deployed PlotLink server: WebP and JPEG. The patch is focused and the required lint-and-typecheck check passed.

Findings

• None.

Decision

Approving. The validation now rejects unsupported image MIME types before forwarding to PlotLink, and the 1.0.27 patch bump is appropriate for this bug fix.