feat(deps): p-retry around Documenso fetch + p-queue installed

p-retry wraps every Documenso API call with 3 attempts (1 + 2 retries),
exponential backoff (1s → 4s with jitter). AbortError short-circuits
on:
- 401/403 — auth failures won't fix themselves on retry
- 4xx other than 429 — Documenso rejected the payload; retrying
  hurts more than it helps

5xx + 429 (rate-limit) go through the retry path with backoff so we
politely re-attempt after delay. Recovers the single-connection-blip
scenario the audit's services pass flagged.

p-queue installed too (audit §36.A.1 companion to p-limit). No
concrete land site today — we don't bulk-fan-out to Documenso, and
existing pLimit covers our internal mass-op fan-outs. Available for
future rate-per-second scenarios.

Verified: tsc clean, vitest 1315/1315.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -91,6 +91,8 @@
     "nodemailer": "^8.0.7",
     "openai": "^6.37.0",
     "p-limit": "^7.3.0",
+    "p-queue": "^9.2.0",
+    "p-retry": "^8.0.0",
     "papaparse": "^5.5.3",
     "pdf-lib": "^1.17.1",
     "pdfjs-dist": "^5.7.284",