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/api/auth/me/route.ts

@@ -14,7 +14,7 @@ export async function GET() {
   }
 
   const { rows } = await pool.query(
-    `SELECT id, email, name, company, status, last_login_at, login_count, created_at, is_showcase
+    `SELECT id, email, name, company, status, last_login_at, login_count, created_at, is_showcase, preferred_lang
      FROM pitch_investors WHERE id = $1`,
     [session.sub]
   )