feat(11-01): implement PAX8 client read-only pagination helpers

- listAllCompanies/listAllSubscriptions/listAllProducts each loop pages via
  the existing fetchJson (inherits 429/Retry-After backoff), size=200
- Shared private paginateAll() helper stops once page.number >= totalPages-1
- Existing listCompanies(page, size) signature unchanged
- GET-only, no mutating method ever set (PAX8-08)

lib/services/pax8-client.ts

@@ -4,7 +4,7 @@
  * https://devx.pax8.com
  */
 
-import type { Pax8Company, Pax8PageEnvelope } from '@/lib/types/pax8';
+import type { Pax8Company, Pax8PageEnvelope, Pax8Subscription, Pax8Product } from '@/lib/types/pax8';
 
 export interface Pax8ClientConfig {
   clientId: string;
@@ -76,4 +76,48 @@ export class Pax8Client {
   async listCompanies(page = 0, size = 10): Promise<Pax8PageEnvelope<Pax8Company>> {
     return this.fetchJson<Pax8PageEnvelope<Pax8Company>>(`/companies?page=${page}&size=${size}`);
   }
+
+  /**
+   * Generic read-only paginate-until-exhausted helper. Loops the given
+   * page-fetcher (each call inherits fetchJson's 429/Retry-After backoff),
+   * requesting size=200, and stops once page.number >= page.totalPages - 1.
+   * GET-only — no method override is ever set, satisfying PAX8-08.
+   */
+  private async paginateAll<T>(
+    fetchPage: (page: number, size: number) => Promise<Pax8PageEnvelope<T>>,
+  ): Promise<T[]> {
+    const size = 200;
+    const items: T[] = [];
+    let page = 0;
+
+    while (true) {
+      const envelope = await fetchPage(page, size);
+      items.push(...envelope.content);
+      if (envelope.page.number >= envelope.page.totalPages - 1) break;
+      page++;
+    }
+
+    return items;
+  }
+
+  /** Read-only: page through every company (PAX8-08 — GET only). */
+  async listAllCompanies(): Promise<Pax8Company[]> {
+    return this.paginateAll<Pax8Company>((page, size) =>
+      this.fetchJson<Pax8PageEnvelope<Pax8Company>>(`/companies?page=${page}&size=${size}`),
+    );
+  }
+
+  /** Read-only: page through every subscription (PAX8-08 — GET only). */
+  async listAllSubscriptions(): Promise<Pax8Subscription[]> {
+    return this.paginateAll<Pax8Subscription>((page, size) =>
+      this.fetchJson<Pax8PageEnvelope<Pax8Subscription>>(`/subscriptions?page=${page}&size=${size}`),
+    );
+  }
+
+  /** Read-only: page through every product (PAX8-08 — GET only). */
+  async listAllProducts(): Promise<Pax8Product[]> {
+    return this.paginateAll<Pax8Product>((page, size) =>
+      this.fetchJson<Pax8PageEnvelope<Pax8Product>>(`/products?page=${page}&size=${size}`),
+    );
+  }
 }