feat(pitch-deck): branded short links for magic URLs (pitch.breakpilot.ai/p/ab3xk2)

- New pitch_short_links table stores 6-char alphanumeric codes mapped to magic link tokens
- GET /p/[code] redirects to /auth/verify?token=... (302, validates expiry)
- All magic link generation points (invite, generate-link, resend) now create a short code
- Emails (invite + resend) use the short URL — less token-like, cleaner for spam filters
- Copy-link UI shows short URL prominently with full URL as fallback
- Migration 008 added to /api/admin/migrate

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

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

@@ -162,6 +162,14 @@ export async function POST(request: NextRequest) {
     `ALTER TABLE dataroom_investor_uploads ADD COLUMN IF NOT EXISTS description_en TEXT`,
     // 007 — investor preferred language
     `ALTER TABLE pitch_investors ADD COLUMN IF NOT EXISTS preferred_lang VARCHAR(5) NOT NULL DEFAULT 'de'`,
+    // 008 — short links for magic URLs
+    `CREATE TABLE IF NOT EXISTS pitch_short_links (
+      id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+      short_code VARCHAR(10) UNIQUE NOT NULL,
+      token VARCHAR(128) NOT NULL,
+      created_at TIMESTAMPTZ DEFAULT NOW()
+    )`,
+    `CREATE INDEX IF NOT EXISTS idx_pitch_short_links_code ON pitch_short_links(short_code)`,
   ]
 
   for (const sql of statements) {