feat(08-01): add getUserPhotoBytes() to MsGraphClient

- New public method fetches binary photo from Graph /users/{id}/photo/$value
- Returns { bytes, contentType } on 200, null on 404 (no photo)
- Throws on other non-2xx for upstream caller to map to 502/503
- Reuses getToken() OAuth2 cache; no retry (best-effort per D-26)
- Existing methods (getToken, fetchJson, getUsers, etc.) untouched

lib/services/msgraph-client.ts

@@ -408,6 +408,35 @@ export class MsGraphClient {
     throw new Error(`Graph move failed ${res.status}: ${text}`);
   }
 
+  /**
+   * Fetch the raw photo bytes for a Microsoft Graph user.
+   * Returns { bytes, contentType } on 200, null when the user has no photo (404),
+   * and throws on any other non-2xx response so the caller can map to 502/503.
+   *
+   * Does NOT reuse fetchJson (which is JSON-only); issues its own fetch for binary data.
+   * No retry logic — photo fetches are best-effort per D-26.
+   */
+  async getUserPhotoBytes(userId: string): Promise<{ bytes: ArrayBuffer; contentType: string } | null> {
+    const token = await this.getToken();
+    const url = `https://graph.microsoft.com/v1.0/users/${encodeURIComponent(userId)}/photo/$value`;
+    const res = await fetch(url, {
+      headers: { Authorization: `Bearer ${token}` },
+    });
+
+    if (res.status === 404) {
+      return null;
+    }
+
+    if (!res.ok) {
+      const text = await res.text().catch(() => '');
+      throw new Error(`Graph photo error ${res.status} for user ${userId}: ${text}`);
+    }
+
+    const bytes = await res.arrayBuffer();
+    const contentType = res.headers.get('content-type') ?? 'image/jpeg';
+    return { bytes, contentType };
+  }
+
   /**
    * Get calendar events for a user in a date range (paginated).
    * Returns empty array and logs if the mailbox is not Exchange Online (graceful degradation).