Add TinyMCE WYSIWYG editor, HTML emails, template DRY refactor, DataT…

[antonio-rodriguez-tam]

Add TinyMCE WYSIWYG editor, HTML emails, template DRY refactor, Datatables fixes

Description:

• Switch to EmailMultiAlternatives with HTML + plain text fallback
• Add TinyMCE editor (self-hosted) for compose, template form, and resend pages
• All body reads/writes go through getBodyContent()/setBodyContent() helpers
• Variable insert uses TinyMCE API with plain textarea fallback
• Preview modals render HTML body (.html() instead of .text(),
  instead of

  )

• Campaign detail sidebar and sent email modal render HTML body
• Auto-select template from ?template=ID URL param on compose page
• Extract 6 shared template includes: _email_preview_modal, _recipient_preview_modal, _delete_confirm_base, _status_badge_td, _stat_card, _danger_zone_card
• Fix nested form bug in variable_form danger zone card
• Fix DataTables crash on empty filtered results (skip init when no data rows)
• Fix DataTables layout: inline Show/Search controls, table outside card body, load Bootstrap4 theme CSS, pagination overflow handling
• Fix aria-hidden warnings on modal close (campaign_detail, resend_compose)
• Campaign detail log table: simple_numbers pagination, default 50 rows

Security Checklist

• Input Validation: All user inputs are properly validated and sanitized to prevent injection attacks.
• Authentication & Authorization: The PR does not introduce unauthorized access, public endpoints or privilege escalation risks.
• Secrets Management: No hardcoded secrets, API keys, or sensitive data are present.
• [X ] Data Protection: Sensitive data is encrypted both at rest and in transit where applicable.
• [X ] Logging & Monitoring: New features include proper logging and monitoring where necessary, without logging sensitive information.
• Security Headers: If applicable, relevant security headers (CSP, HSTS, X-Frame-Options) are correctly configured.
• [X ] Error Handling: Errors do not expose sensitive system details.
• [X ] Third-Party Services: Any new third-party integrations follow security best practices (e.g. authentication, encryption, logging).
• [X ] Code Review: The PR has been reviewed for potential security flaws.

---

Additional Notes

Checklist

• [X ] I have performed a self-review of my code
• [X ] I have tested the changes locally
• I have run security tests where applicable
• [X ] This PR follows the coding and security guidelines of the project

[claire-peters]

Tested sending of formatted emails on dev and it worked without issue.