release(v4.0.0): Shade GA — V3.x consolidation + audit prep

V3.1 → V3.12 consolidated and tagged for the first GA release. Wire
format unchanged from 0.4.x — 4.0 peers interoperate with 0.4.x peers
byte-for-byte. The version bump is semantic: audit-cycle complete,
opt-in surface fully exposed, threat model refreshed for every new
surface.

Highlights:
- All 24 @shade/* packages bumped to 4.0.0 in lockstep.
- CHANGELOG 4.0.0 section is the canonical manifest of what landed.
- THREAT-MODEL extended (§10 fingerprint gates, §11 WebRTC P2P, §12
  Web-Worker boundary) + residual-risks table refreshed.
- OpenAPI now covers all 27 routes: prekey, transfer, KT, inbox,
  bridge, observer, /metrics, /healthz, /ready.
- MIGRATION 0.3.x → 4.0 documented + smoke-tested against
  shade migrate-storage on a real SQLite DB.
- docs/audit/REVIEW-BUNDLE.md + SCOPE.md ready for external reviewer.
- scripts/soak.ts harness for the GA-stable 2-week soak window.
- All V*.md plans archived under docs/archive/ with Status: Done.
- Voice/Video carved out into V5.0; 4.0 audit focuses on the frozen
  non-realtime stack.

Tests: TS 1000/1000 + Kotlin 11/11 cross-platform vectors green.
Docker: gt.zyon.no/stian/shade-prekey:4.0.0 builds and reports
  version 4.0.0 on /health.

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

test-vectors/backup.json

@@ -0,0 +1,20 @@
+{
+  "version": 2,
+  "vectors": [
+    {
+      "description": "Backup v1: HKDF(passphrase_utf8, salt, info=\"ShadeBackupKey\", 32) -> backupKey",
+      "passphrase": "correct-horse-battery-staple",
+      "salt": "a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5",
+      "info": "ShadeBackupKey",
+      "backupKey": "ee14b1292de8761db52cfdb5e4e24d8c165d5f2a5268c8d0ac6da51e291d027f"
+    },
+    {
+      "description": "Backup v1: AES-256-GCM(backupKey, plaintext, no AAD) with deterministic nonce",
+      "backupKey": "ee14b1292de8761db52cfdb5e4e24d8c165d5f2a5268c8d0ac6da51e291d027f",
+      "nonce": "c7c7c7c7c7c7c7c7c7c7c7c7",
+      "plaintext": "7b2276657273696f6e223a312c226964656e74697479223a6e756c6c2c2273657373696f6e73223a5b5d7d",
+      "plaintextUtf8": "{\"version\":1,\"identity\":null,\"sessions\":[]}",
+      "ciphertext": "2605b2494fff14d4151e1a22da0740f4d13631a046498f588cf281febe40f1671f4e07978ea183b20ebfbe9ca2e638f06c9d443e550a587e2460d1"
+    }
+  ]
+}