refactor(server): replace node-fetch with native fetch + undici, fix photo integrations

Replace node-fetch v2 with Node 22's built-in fetch API across the entire server.
Add undici as an explicit dependency to provide the dispatcher API needed for
DNS pinning (SSRF rebinding prevention) in ssrfGuard.ts. All seven service files
that used a plain `import fetch from 'node-fetch'` are updated to use the global.
The ssrfGuard safeFetch/createPinnedAgent is rewritten as createPinnedDispatcher
using an undici Agent, with correct handling of the `all: true` lookup callback
required by Node 18+. The collabService dynamic require() and notifications agent
option are updated to use the dispatcher pattern. Test mocks are migrated from
vi.mock('node-fetch') to vi.stubGlobal('fetch'), and streaming test fixtures are
updated to use Web ReadableStream instead of Node Readable.

Fix several bugs in the Synology and Immich photo integrations:
- pipeAsset: guard against setting headers after stream has already started
- _getSynologySession: clear stale SID and re-login when decrypt_api_key returns null
  instead of propagating success(null) downstream
- _requestSynologyApi: return retrySession error (not stale session) on retry failure;
  also retry on error codes 106 (timeout) and 107 (duplicate login), not only 119
- searchSynologyPhotos: fix incorrect total field type (Synology list_item returns no
  total); hasMore correctly uses allItems.length === limit
- _splitPackedSynologyId: validate cache_key format before use; callers return 400
- getImmichCredentials / _getSynologyCredentials: treat null from decrypt_api_key as
  a missing-credentials condition rather than casting null to string
- Synology size param: enforce allowlist ['sm', 'm', 'xl'] per API documentation

server/tests/unit/services/notificationService.test.ts

@@ -47,11 +47,11 @@ vi.mock('nodemailer', () => ({
   },
 }));
 
-vi.mock('node-fetch', () => ({ default: fetchMock }));
+vi.stubGlobal('fetch', fetchMock);
 vi.mock('../../../src/websocket', () => ({ broadcastToUser: broadcastMock }));
 vi.mock('../../../src/utils/ssrfGuard', () => ({
   checkSsrf: vi.fn(async () => ({ allowed: true, isPrivate: false, resolvedIp: '1.2.3.4' })),
-  createPinnedAgent: vi.fn(() => ({})),
+  createPinnedDispatcher: vi.fn(() => ({})),
 }));
 
 import { createTables } from '../../../src/db/schema';
@@ -109,6 +109,7 @@ beforeEach(() => {
 
 afterAll(() => {
   testDb.close();
+  vi.unstubAllGlobals();
 });
 
 // ─────────────────────────────────────────────────────────────────────────────

server/tests/unit/services/notifications.test.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect, vi, afterEach, beforeEach } from 'vitest';
+import { describe, it, expect, vi, afterEach, afterAll, beforeEach } from 'vitest';
 
 vi.mock('../../../src/db/database', () => ({
   db: { prepare: () => ({ get: vi.fn(() => undefined), all: vi.fn(() => []) }) },
@@ -16,12 +16,12 @@ vi.mock('../../../src/services/auditLog', () => ({
   getClientIp: vi.fn(),
 }));
 vi.mock('nodemailer', () => ({ default: { createTransport: vi.fn(() => ({ sendMail: vi.fn() })) } }));
-vi.mock('node-fetch', () => ({ default: vi.fn() }));
+vi.stubGlobal('fetch', vi.fn());
 
 // ssrfGuard is mocked per-test in the SSRF describe block; default passes all
 vi.mock('../../../src/utils/ssrfGuard', () => ({
   checkSsrf: vi.fn(async () => ({ allowed: true, isPrivate: false, resolvedIp: '1.2.3.4' })),
-  createPinnedAgent: vi.fn(() => ({})),
+  createPinnedDispatcher: vi.fn(() => ({})),
 }));
 
 import { getEventText, buildEmailHtml, buildWebhookBody, sendWebhook } from '../../../src/services/notifications';
@@ -253,7 +253,7 @@ describe('sendWebhook SSRF protection (SEC-017)', () => {
   });
 
   it('allows a public URL and calls fetch', async () => {
-    const mockFetch = (await import('node-fetch')).default as unknown as ReturnType<typeof vi.fn>;
+    const mockFetch = globalThis.fetch as unknown as ReturnType<typeof vi.fn>;
     mockFetch.mockResolvedValueOnce({ ok: true, text: async () => '' } as never);
     vi.mocked(checkSsrf).mockResolvedValueOnce({ allowed: true, isPrivate: false, resolvedIp: '1.2.3.4' });
 
@@ -306,7 +306,7 @@ describe('sendWebhook SSRF protection (SEC-017)', () => {
   });
 
   it('does not call fetch when SSRF check blocks the URL', async () => {
-    const mockFetch = (await import('node-fetch')).default as unknown as ReturnType<typeof vi.fn>;
+    const mockFetch = globalThis.fetch as unknown as ReturnType<typeof vi.fn>;
     mockFetch.mockClear();
     vi.mocked(checkSsrf).mockResolvedValueOnce({
       allowed: false, isPrivate: true, resolvedIp: '127.0.0.1',
@@ -317,3 +317,5 @@ describe('sendWebhook SSRF protection (SEC-017)', () => {
     expect(mockFetch).not.toHaveBeenCalled();
   });
 });
+
+afterAll(() => vi.unstubAllGlobals());

server/tests/unit/services/weatherService.test.ts

@@ -1,10 +1,12 @@
-import { describe, it, expect, vi, beforeAll } from 'vitest';
+import { describe, it, expect, vi, beforeAll, afterAll } from 'vitest';
 
 // Prevent the module-level setInterval from running during tests
 vi.useFakeTimers();
 
-// Mock node-fetch to prevent real HTTP requests
-vi.mock('node-fetch', () => ({ default: vi.fn() }));
+// Prevent real HTTP requests
+vi.stubGlobal('fetch', vi.fn());
+
+afterAll(() => vi.unstubAllGlobals());
 
 import { estimateCondition, cacheKey } from '../../../src/services/weatherService';