feat: add web UI with login, CRUD, admin, and API key management

- Add login page with JWT authentication
- Add dashboard with stats and quick actions
- Add links management page (full CRUD with search)
- Add collections management page
- Add API key management page with copy-to-clipboard
- Add admin user management page (admin only)
- Fix UUID type mismatches across all endpoints
- Add updated_at column to api_keys and audit_log in schema.sql
- Fix DB_PASSWORD default in docker-compose.yml
- Add PyJWT to requirements.txt
- Fix API docs URL (/docs instead of /api/docs)
- Improve JS error handling (show actual messages)
- Rewrite conftest.py with proper DB lifecycle management
- Add 42 new integration tests (84 total, all passing)
  - test_admin.py: 15 tests for admin endpoints
  - test_auth_extended.py: 9 tests for API key CRUD
  - test_tags.py: 12 tests for tag endpoints
  - test_sync.py: 6 tests for sync endpoints

LinkSyncServer/tests/test_sync.py

@@ -0,0 +1,93 @@
+"""
+LinkSyncServer - Sync API Tests
+"""
+
+import uuid
+import pytest
+from fastapi.testclient import TestClient
+
+
+class TestSync:
+    def test_sync_list_collections(self, client: TestClient):
+        response = client.get("/api/sync/collections")
+        assert response.status_code == 200
+        assert isinstance(response.json(), list)
+
+    def test_sync_get_collection_not_found(self, client: TestClient, auth_headers: dict):
+        response = client.get(
+            "/api/sync/collections/00000000-0000-0000-0000-000000000000",
+            headers=auth_headers,
+        )
+        assert response.status_code == 404
+
+    def test_sync_create_collection_and_get(self, client: TestClient, auth_headers: dict):
+        col_name = f"Sync Get Test {uuid.uuid4().hex[:8]}"
+        create_resp = client.post(
+            "/api/collections/",
+            json={
+                "name": col_name,
+                "description": "Test",
+                "query_type": "static",
+                "is_public": False,
+                "link_ids": [],
+            },
+            headers=auth_headers,
+        )
+        collection_id = create_resp.json()["id"]
+        response = client.get(
+            f"/api/sync/collections/{collection_id}",
+            headers=auth_headers,
+        )
+        assert response.status_code == 200
+        assert response.json()["name"] == col_name
+
+    def test_sync_add_links(self, client: TestClient, auth_headers: dict, sample_bookmark_data: dict):
+        bm_data = sample_bookmark_data.copy()
+        bm_data["url"] = f"https://sync-test-{uuid.uuid4().hex[:8]}.com"
+        bm_data["title"] = f"Sync Test {uuid.uuid4().hex[:8]}"
+        bm_resp = client.post("/api/links/", json=bm_data, headers=auth_headers)
+        bookmark_id = bm_resp.json()["id"]
+
+        col_name = f"Sync Add Links {uuid.uuid4().hex[:8]}"
+        col_resp = client.post(
+            "/api/collections/",
+            json={
+                "name": col_name,
+                "query_type": "static",
+                "is_public": False,
+                "link_ids": [],
+            },
+            headers=auth_headers,
+        )
+        collection_id = col_resp.json()["id"]
+
+        response = client.post(
+            f"/api/sync/collections/{collection_id}/add-links",
+            json=[bookmark_id],
+            headers=auth_headers,
+        )
+        assert response.status_code == 200
+
+    def test_sync_delete_collection(self, client: TestClient, auth_headers: dict):
+        col_name = f"Sync Delete {uuid.uuid4().hex[:8]}"
+        create_resp = client.post(
+            "/api/collections/",
+            json={
+                "name": col_name,
+                "query_type": "static",
+                "is_public": False,
+                "link_ids": [],
+            },
+            headers=auth_headers,
+        )
+        collection_id = create_resp.json()["id"]
+
+        response = client.delete(
+            f"/api/sync/collections/{collection_id}",
+            headers=auth_headers,
+        )
+        assert response.status_code == 200
+
+    def test_sync_list_collections_no_auth(self, client: TestClient):
+        response = client.get("/api/sync/collections")
+        assert response.status_code == 200