feat(pitch-deck): English email templates, investor language preference, link-only invite mode

- Add English email template variants (greeting, message, closing, subject, CTA copy)
- Add `preferred_lang` column to `pitch_investors` — stored per investor, deck opens in that language by default
- Invite form: DE/EN language toggle that switches email defaults and pitch language setting
- Invite form: "Send email" toggle — when off, creates investor + returns magic link without sending email (for cold outreach attachment)
- `app/page.tsx`: initializes pitch language from investor's `preferred_lang` before first render (no flash)
- Migration 007 added to `/api/admin/migrate` route for production rollout

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pitch-deck/app/page.tsx

@@ -1,19 +1,29 @@
 'use client'
 
-import { useState, useCallback } from 'react'
+import { useState, useCallback, useEffect, useRef } from 'react'
 import { Language } from '@/lib/types'
 import { useAuth } from '@/lib/hooks/useAuth'
 import PitchDeck from '@/components/PitchDeck'
 
 export default function Home() {
-  const [lang, setLang] = useState<Language>('de')
   const { investor, loading, logout } = useAuth()
+  const [lang, setLang] = useState<Language>('de')
+  const [langReady, setLangReady] = useState(false)
+  const synced = useRef(false)
+
+  useEffect(() => {
+    if (!loading && !synced.current) {
+      synced.current = true
+      if (investor?.preferred_lang === 'en') setLang('en')
+      setLangReady(true)
+    }
+  }, [loading, investor])
 
   const toggleLanguage = useCallback(() => {
     setLang(prev => prev === 'de' ? 'en' : 'de')
   }, [])
 
-  if (loading) {
+  if (loading || !langReady) {
     return (
       <div className="h-screen flex items-center justify-center">
         <div className="w-12 h-12 border-2 border-indigo-500 border-t-transparent rounded-full animate-spin" />