Add passkey (WebAuthn) authentication with self-registration

Enable users to sign up and sign in using passkeys (biometrics/security
keys) without needing a manually-created Authentik account. The existing
SSO login remains as an alternative.

Backend:
- Add WebAuthn registration/authentication endpoints via py-webauthn
- Issue HS256 JWTs for passkey users, with Redis-backed challenge storage
- Dual JWT verification in auth middleware (issuer-based routing: passkey
  HS256 vs Authentik RS256)
- PasskeyCredential model + migration making user.password nullable
- UserRepository with full CRUD for users and credentials

Frontend:
- AuthUser type abstraction unifying OIDC and passkey users
- Passkey service using @simplewebauthn/browser for WebAuthn ceremonies
- LoginModal redesigned with Sign In / Sign Up tabs
- Type migration from oidc-client-ts User to AuthUser across all services
  and components

crawler/frontend/src/services/taskService.ts

@@ -1,6 +1,6 @@
 // Task service for fetching task status
 
-import type { User } from 'oidc-client-ts';
+import type { AuthUser } from '@/auth/types';
 import type { TaskStatusResponse } from '@/types';
 import { apiRequest } from './apiClient';
 import { API_ENDPOINTS } from '@/constants';
@@ -19,7 +19,7 @@ export interface ClearAllTasksResponse {
 /**
  * Fetch all active tasks for the current user
  */
-export async function fetchTasksForUser(user: User): Promise<string[]> {
+export async function fetchTasksForUser(user: AuthUser): Promise<string[]> {
   return apiRequest<string[]>(user, API_ENDPOINTS.TASKS_FOR_USER);
 }
 
@@ -27,7 +27,7 @@ export async function fetchTasksForUser(user: User): Promise<string[]> {
  * Fetch the status of a specific task
  */
 export async function fetchTaskStatus(
-  user: User,
+  user: AuthUser,
   taskId: string
 ): Promise<TaskStatusResponse> {
   return apiRequest<TaskStatusResponse>(user, API_ENDPOINTS.TASK_STATUS, {
@@ -39,7 +39,7 @@ export async function fetchTaskStatus(
  * Cancel a running task
  */
 export async function cancelTask(
-  user: User,
+  user: AuthUser,
   taskId: string
 ): Promise<CancelTaskResponse> {
   return apiRequest<CancelTaskResponse>(user, API_ENDPOINTS.CANCEL_TASK, {
@@ -51,7 +51,7 @@ export async function cancelTask(
 /**
  * Clear all tasks for the current user
  */
-export async function clearAllTasks(user: User): Promise<ClearAllTasksResponse> {
+export async function clearAllTasks(user: AuthUser): Promise<ClearAllTasksResponse> {
   return apiRequest<ClearAllTasksResponse>(user, API_ENDPOINTS.CLEAR_ALL_TASKS, {
     method: 'POST',
   });