[CHORE]: Add field focus out validation to forms

[gcgoncalves]

🔧 Chore Summary

Add a validation function to add a red border and an error message to invalid fields on focus out.

Provide a brief summary of the maintenance task or internal tooling update you're proposing or working on.

---

🧱 Area Affected

Choose the general area(s) that this chore affects:

• GitHub Actions / CI Pipelines
• Pre-commit hooks / linters
• Formatting (black, isort, ruff, etc.)
• Type-checking (mypy, pyright, pytype, etc.)
• Dependency cleanup or updates
• Build system or Makefile
• Containerization (Docker/Podman)
• Docs or spellcheck
• SBOM, CVE scans, licenses, or security checks
• Other: Admin UI

---

⚙️ Context / Rationale

Giving users real-time field validation (without causing the focus lock reported on #1916

---

📋 Acceptance Criteria

Define what "done" looks like for this task.

• Focusing out of a required field triggers validation and displays a relevant error message.
• User focus out of a required field without focus getting trapped