feat(pitch-admin): generate magic link + 72h investor data masking

- New POST /api/admin/investors/[id]/generate-link endpoint: creates a
  magic link without sending email, returns the URL for the admin to
  copy and share manually (for when email is filtered)
- Adds 'Copy Link' button (emerald) to investor list and detail pages;
  link is copied to clipboard on click
- New lib/masking.ts: maskOverdueInvestors() UPDATE that anonymizes
  email/name/company → revokes sessions 72h after first investor login
- first_activity_at recorded on first verify (COALESCE, set once only)
- migration 004 adds first_activity_at + data_masked_at columns with
  partial index; also wired into /api/admin/migrate for one-shot apply
- Admin UI shows 'anonymized' badge, expiry countdown, and masked state;
  Copy Link + Resend are disabled for anonymized investors
- verify route returns 410 if data_masked_at is set (belt-and-suspenders
  alongside the revoked status check)

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

pitch-deck/migrations/004_investor_masking.sql

@@ -0,0 +1,9 @@
+-- Investor data masking: track first activity and enforce 72h anonymization window
+ALTER TABLE pitch_investors
+  ADD COLUMN IF NOT EXISTS first_activity_at TIMESTAMPTZ,
+  ADD COLUMN IF NOT EXISTS data_masked_at TIMESTAMPTZ;
+
+-- Partial index for fast masking-eligibility scans
+CREATE INDEX IF NOT EXISTS idx_pitch_investors_mask_check
+  ON pitch_investors (first_activity_at)
+  WHERE first_activity_at IS NOT NULL AND data_masked_at IS NULL;