feat(frontend): show app version

[dataforxyz]

• What kind of change does this PR introduce?
  Feature – exposes the current app version in the Settings page by wiring the build/version metadata through Next.js.
• Why was this change needed?
  The Settings screen lacked visibility into which build was deployed, making debugging and support harder. By threading the version through NEXT_PUBLIC_APP_VERSION (reading from version.txt or an env var) and rendering it in Global Settings, support and QA can confirm the exact build without external tooling. No related GitHub issue reference was provided.
• Other information:
  No prior discussions were needed; this is a contained UI enhancement. Future follow-up could include surfacing the version in more discovery-friendly areas (e.g., footer) or linking to release notes, but that’s out of scope here.
• Checklist:
  • I have read the CONTRIBUTING (https://github.com/gitroomhq/postiz-app/blob/main/CONTRIBUTING.md) guide.
  • I checked that there were not similar issues or PRs already open for this.
  • This PR fixes just ONE issue (do not include multiple issues or types of change in the same PR).

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