Fix publish race error toast

[naaiyy]

Summary

• prefer Convex structured error data over the transport wrapper
• keep empty Convex envelopes out of user-facing toasts
• cover stale-draft and empty-envelope cases

Verification

• bun test
• bun run check-types
• bunx biome check apps/web/features/editor/publish-dialog.tsx apps/web/features/editor/publish-dialog.test.ts

[vercel]

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Project	Deployment	Actions	Updated (UTC)
base-blocks	Ready	Preview	Aug 28, 2026 9:19pm

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit 8dfc7a5.}