wip(intake): router, enrich endpoint, Slack handlers, migration 0034 — UNTESTED checkpoint

Agent was terminated by the session usage limit before running lint/tests or
writing its report. Files are complete drafts against plan §11 (C1, C2, C5):
src/app/api/intake/, src/app/api/transactions/[id]/line-items/, src/lib/intake-*.ts,
src/lib/line-items.ts, prisma/migrations/0034_intake_batches, fixtures + tests.
Next: npm ci && npx prisma generate && npm run lint && npm test && npm run test:integration.

package.json

@@ -23,7 +23,8 @@
     "prisma": "^7.4.2",
     "react": "19.2.3",
     "react-dom": "19.2.3",
-    "recharts": "^3.8.0"
+    "recharts": "^3.8.0",
+    "unpdf": "^1.8.1"
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",