fix: harden editor and sync edge cases

[ShiroKSH]

Summary

• Prevent active-link ranges from merging adjacent links with different attributes.
• Preserve mixed task and plain list items when toggling list type.
• Preserve trailing text after inline Markdown images.
• Prevent duplicate debounced saves and make desktop persistence best-effort.
• Reject failed asset upload and download responses before updating sync state.
• Remove the Unix-only CLI postbuild step so Windows CLI builds succeed.

Validation

• pnpm test: 175 tests passed.
• pnpm build passed.
• pnpm check passed.
• pnpm typecheck passed.

Scope

This change keeps the existing sync and workspace contracts intact. Server-side authentication, ownership, path validation, and conflict resolution remain separate follow-up work.

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[bholmesdev]

Thanks for the batch of fixes, these are all real bugs. Two notes:

1. I pushed a commit to this branch (fed659c). The trailing-text image fix dropped the image node to alt text, so ![diagram](example.png) trailing would rewrite the user's file as diagram trailing on the next save, losing the image reference. Images are block nodes in the editor schema, so the paragraph now splits around image children: the image survives as a block and the surrounding text becomes paragraphs. Also added a console.warn to the localStorage catch so quota/security failures are visible.

2. The new res.ok throws in sync.ts are the right direction, but no call site catches, so one failed asset aborts the whole sync before state is written, and in hubble cloud watch it becomes an unhandled rejection that kills the watcher. Tracked as a follow-up in Cloud sync: one failed asset transfer aborts the whole run and can crash hubble cloud watch #161, no change needed here.