fix: PermissionError on Email Queue for non-admin users

[one-fm]

Summary

Fixed PermissionError on Email Queue for non-admin users by bypassing UI-level permission checks during background email sending.

Changes

• one_fm/events/email_queue.py:
  • Added send_mail(name) function to fetch Email Queue doc and call doc.send() directly. This avoids the check_permission call inside the whitelisted send_now function.
  • Updated after_insert hook to enqueue send_mail instead of send_now.
  • Updated flush_emails to use frappe.get_all (bypassing list permissions) and send_mail.

Review Checklist

• validate_doctype_json: ✅ N/A (No JSON changes)
• bench migrate: ❌ FAILED (Unrelated patch error in one_fm.patches.v15_0.fix_leave_allocation_carry_forward_hr_emp_02814. This patch fails because it expects a specific record HR-LAL-2024-01853 which is missing in the environment.)
• run_tests: ✅ PASS
• hooks.py paths verified: ✅ one_fm.events.email_queue.after_insert
• No frappe.db.commit() in controllers: ✅ flush_emails is a utility/background function.

How to Verify

1. Log in as a non-admin user.
2. Trigger an email (e.g., by adding a comment to an Issue).
3. Verify the email is enqueued and sent without PermissionError in background jobs.

Closes #6020