Fix create_prompt is_public bug, conditional version bump, and add Jotai prompts atoms

- Pass is_public from request body in create_prompt route
- Only bump version on content field changes (name, prompt, mode),
  not on is_public toggle
- Add prompts query and mutation atoms (atomWithQuery/atomWithMutation)
  with TanStack Query caching, replacing manual useEffect fetches
- Update PromptPicker, PromptsContent, and CommunityPromptsContent
  to consume shared atoms instead of local state