Task: Add project cover upload to review dialog

Identity

Add a required project-cover picker and preview to the first-submission information dialog.
Validate and encode PNG/JPEG/WebP input in Renderer, then pass the existing bounded cover DTO through the Main-owned publish route.
Update Electron Main to call the new Works Square atomic metadata-plus-cover create contract before version upload.
Preserve version-only behavior and existing metadata/cover for draft and published Works projects.

Renderer may handle only the user-selected cover bytes and safe metadata; Works credentials, local project paths, archives, build output, and idempotency stay in Electron Main.
First submission requires one valid cover and must fail before source upload if the atomic create contract rejects it.
Do not restore a standalone publish/upload page or cloud-deploy workbench.
Do not use the old standalone cover-upload-plus-JSON-create sequence, which can leave orphaned objects or lose a 404-to-409 race.
Feature mode updates only this task record in canonical project memory; README stays synchronized with the user-visible behavior.

The first-submission information dialog now requires a PNG, JPEG, or WebP cover no larger than 10 MiB and shows its preview, file name, and a reselect action.
Renderer validates MIME type, non-empty size, byte limit, and file signature before passing the existing bounded cover DTO to Electron Main.
Electron Main now sends metadata JSON and cover in one POST /api/projects/with-cover multipart request, retaining ownership of credentials, paths, archives, and version upload.
A create conflict stops before version upload; existing draft and published projects continue through the version-only path without replacing their cover.
README now describes the required first-submission cover and the multipart create flow.
The shared Electron E2E now covers opening the first-submission dialog, the missing-cover error, a valid PNG preview, the selected file name, and the reselect action.

Focused Vitest run for project-publish-action, works-routes, and works-square — 3 files, 76 tests passed.
tsc --noEmit — passed.
Focused ESLint on all changed TypeScript/TSX files — passed.
Vite production build — passed; only pre-existing dynamic-import and chunk-size warnings were emitted.
Focused Playwright run for tests/e2e/project-configuration-skills.spec.ts — 1 passed.
git diff --check — passed with only the repository's Windows LF-to-CRLF notices.

Integrate and deploy the matching Works Square server task 20260817-project-cover-upload-0cc3cb72 before distributing a client that calls the new route.
Non-blocking hardening: add direct Renderer/Main unit cases for empty or signature-mismatched files, and assess explicit Host JSON-body and cover-file-name length limits with the broader Host API boundary.