feat: add send test email for templates and use draft content

[hanamizuki]

Summary

• Add "Send Test Email" feature for templates, matching the existing campaign test email UI and functionality
• Update both template and campaign test email endpoints to accept optional draft fields (subject, body, from, fromName, replyTo), so test emails reflect the current editor content without requiring a save first

Changes

New: Template Send Test Email

• apps/api/src/controllers/Templates.ts — new POST /templates/:id/test endpoint
• apps/api/src/services/TemplateService.ts — sendTest() method with draft content support
• apps/web/src/pages/templates/[id].tsx — Send Test button, dialog, and project member selector

Fix: Use draft content for test emails

• apps/api/src/services/CampaignService.ts — accept optional draft param, use draft fields when present
• apps/api/src/controllers/Campaigns.ts — pass draft fields from request body to service
• apps/web/src/pages/campaigns/[id].tsx — send current editor content with test email request

Test plan

• Open a template, modify subject/body without saving, send test email → verify test email uses the unsaved content
• Open a campaign, modify subject/body without saving, send test email → verify test email uses the unsaved content
• Send test email without any unsaved changes → verify it still works (falls back to DB content)
• Verify test emails can only be sent to project members

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