feat(pitch-deck): bilingual email template + invite page with live preview

Email template (email.ts):
- Bilingual: German body + DE/EN legal footer
- Customizable greeting, message body, and closing
- Magic Link explanation box (hardcoded)
- Confidentiality & Disclaimer footer (hardcoded, bilingual)

Invite page (investors/new):
- Name is now required, Company is optional
- Editable fields: greeting, message, closing (with defaults)
- Live email preview panel (right side)
- Shows full email content before sending
- German UI labels

API (invite/route.ts):
- Passes greeting, message, closing to email function

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pitch-deck/app/api/admin/invite/route.ts

@@ -11,7 +11,7 @@ export async function POST(request: NextRequest) {
   const adminId = guard.kind === 'admin' ? guard.admin.id : null
 
   const body = await request.json().catch(() => ({}))
-  const { email, name, company } = body
+  const { email, name, company, greeting, message, closing } = body
 
   if (!email || typeof email !== 'string') {
     return NextResponse.json({ error: 'Email required' }, { status: 400 })
@@ -54,7 +54,7 @@ export async function POST(request: NextRequest) {
   const baseUrl = process.env.PITCH_BASE_URL || 'https://pitch.breakpilot.ai'
   const magicLinkUrl = `${baseUrl}/auth/verify?token=${token}`
 
-  await sendMagicLinkEmail(normalizedEmail, name || null, magicLinkUrl)
+  await sendMagicLinkEmail(normalizedEmail, name || null, magicLinkUrl, greeting, message, closing)
 
   await logAdminAudit(
     adminId,