Set manifest.json isDesktopOnly to true

[RE-codes]

Story

As a maintainer, before MVP completion, the manifest should declare desktop-only since mobile behavior is unverified and not personally needed. The current value is false.

Tasks

• Edit manifest.json and set isDesktopOnly from false to true.
• Run npm run build and verify the build still succeeds.
• Reload the plugin in the desktop vault to confirm it still loads.
• Mobile re-enable, if desired later, is tracked in Epic 12 (P3) child "Mobile support decision".

Acceptance Criteria

• manifest.json shows "isDesktopOnly": true.
• Plugin loads in the desktop vault.
• README's installation/limitations section calls out desktop-only support.

References

• Parent epic: Epic: MVP Completion Gate #98
• plan/codebase-architecture-analysis.md § Product Direction — bullet on mobile