Add authentication and authorization to template endpoints

[coderabbitai]

Description

Add authentication and authorization checks to template API endpoints to ensure only authorized users can perform operations like deletion.

Context

During review of PR #67, it was identified that the template endpoints lack proper authorization checks. A TODO was added to address this in a future PR.

Scope

• Implement authentication middleware or decorators for template endpoints
• Add authorization checks for the DELETE /template.delete endpoint to verify:
  • User is authenticated
  • User is authorized to delete the template (owner or admin)
• Review and secure other template endpoints as needed (POST /template.create, POST /template.materialize, etc.)

Security Impact

Without authorization, any authenticated user could potentially delete templates they don't own, which is a security concern.

References

• PR: Genie 1171/story/create template system #67
• Review Comment: Genie 1171/story/create template system #67 (comment)
• File: multi-agent/api/flask/endpoints/templates.py
• Endpoint: delete_template (lines 184-216)

Requested by

@odaiodeh