feat: verify context attestations via ES256/JWKS + rename client to appshell-crm

Proof #3 now supports the production asymmetric path, not just the dev shared secret.

- context-attestation.ts: PublicKeyResolverPort seam; verify() picks ES256 (JWKS by
  kid) when the client has a jwksUri, else HS256 (dev). signDevAttestationES256 helper.
- attestation-stores.ts: JwksPublicKeyResolver (jwks-rsa, one cached client per URI,
  refetch on rotation, fail-closed to NO_KEY).
- attestation.module.ts: inject the resolver into the verifier; dev-seed the client as
  clientType APPSHELL (it is the CRM browser-flow parent per the July-12 notes).
- rename the registered client crm-support-widget -> appshell-crm (the name reflects the
  attesting parent, not a widget).
- specs: ES256 (valid via JWKS, wrong key -> BAD_SIGNATURE, unknown kid -> NO_KEY, no
  resolver -> NO_KEY) + two stolen-token gate cases (wrong app binding -> APP_MISMATCH,
  wrong audience -> WRONG_AUDIENCE).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/src/platform/attestation-stores.ts

@@ -1,7 +1,13 @@
 import { Injectable } from '@nestjs/common';
 import { Prisma } from '@prisma/client';
+import { JwksClient } from 'jwks-rsa';
 import { PrismaService } from '../prisma/prisma.service';
-import type { ClientRegistryEntry, ClientRegistryPort, NonceStorePort } from './context-attestation';
+import type {
+  ClientRegistryEntry,
+  ClientRegistryPort,
+  NonceStorePort,
+  PublicKeyResolverPort,
+} from './context-attestation';
 
 /** Client registry backed by Postgres (IiosClientRegistry). */
 @Injectable()
@@ -40,3 +46,31 @@ export class PrismaNonceStore implements NonceStorePort {
     }
   }
 }
+
+/**
+ * Resolves a client's public signing key from its JWKS (prod ES256 path). Keeps ONE JwksClient
+ * per jwksUri — the client caches keys and refetches on a cache miss (so key rotation is picked up
+ * without a restart). Returns null on any failure so the verifier fails closed with NO_KEY.
+ */
+@Injectable()
+export class JwksPublicKeyResolver implements PublicKeyResolverPort {
+  private readonly clients = new Map<string, JwksClient>();
+
+  private clientFor(jwksUri: string): JwksClient {
+    let c = this.clients.get(jwksUri);
+    if (!c) {
+      c = new JwksClient({ jwksUri, cache: true, cacheMaxEntries: 8, cacheMaxAge: 10 * 60_000, rateLimit: true, jwksRequestsPerMinute: 12 });
+      this.clients.set(jwksUri, c);
+    }
+    return c;
+  }
+
+  async resolve(jwksUri: string, kid: string): Promise<string | null> {
+    try {
+      const key = await this.clientFor(jwksUri).getSigningKey(kid);
+      return key.getPublicKey(); // PEM (SPKI) — works for EC (ES256) and RSA keys
+    } catch {
+      return null; // unknown kid / unreachable JWKS / malformed key → fail closed
+    }
+  }
+}