Flatten repo structure: move crawler/ to root, remove vqa/ and immoweb/

The crawler subdirectory was the only active project. Moving it to the
repo root simplifies paths and removes the unnecessary nesting. The
vqa/ and immoweb/ directories were legacy/unused and have been removed.

Updated .drone.yml, .gitignore, .claude/ docs, and skills to reflect
the new flat structure.

frontend/src/auth/authService.ts

@@ -0,0 +1,45 @@
+import { User, UserManager } from 'oidc-client-ts';
+import { oidcConfig } from './config';
+import { parseOidcError, type AuthError } from './errors';
+
+const userManager = new UserManager(oidcConfig);
+
+export const login = async (): Promise<void> => {
+    try {
+        await userManager.signinRedirect();
+    } catch (error) {
+        console.error('Login redirect failed:', error);
+        throw parseOidcError(error);
+    }
+};
+
+export const logout = async (): Promise<void> => {
+    try {
+        await userManager.signoutRedirect();
+    } catch (error) {
+        console.error('Logout redirect failed:', error);
+        throw parseOidcError(error);
+    }
+};
+
+export const handleCallback = async (): Promise<User> => {
+    try {
+        const user = await userManager.signinRedirectCallback();
+        return user;
+    } catch (error) {
+        console.error('Callback handling failed:', error);
+        throw parseOidcError(error);
+    }
+};
+
+export const getUser = async (): Promise<User | null> => {
+    try {
+        const user = await userManager.getUser();
+        return user;
+    } catch (error) {
+        console.error('Error fetching user:', error);
+        return null;
+    }
+};
+
+export type { AuthError };