Fix calendar booking step in onboarding when env var is not configured (#14707)

## The Issue

When CALENDAR_BOOKING_PAGE_ID env variable is not configured, the
onboarding flow still sets the booking step as pending in the database.
This causes users to get stuck on a broken booking page after
logout/login, as the Cal.com iframe tries to load with an empty calendar
link.

 ## The Fix

Made the booking step handling idempotent across the stack:

  Backend:
- setOnboardingBookOnboardingPending now checks if calendar is actually
configured before setting the step as pending
- getOnboardingStatus auto-cleans invalid booking states when detected
(booking pending but no calendar configured)
  - Empty strings in env are now treated as undefined in client config

  Frontend:
- Added navigation protection to redirect away from booking pages when
calendar isn't configured
- Existing defensive logic in useSetNextOnboardingStatus already skips
booking when no calendar ID

  Result

  - New users won't get invalid booking states
  - Existing bad data self-heals when users interact with the system
  - Backend and frontend stay in sync about when booking should be shown

Fixes the issue Felix reported where users saw a broken booking page in
production.
  
I think we should keep the old CAL_LINK constant for now - while we
could remove the booking onboarding step entirely, it would break the
plan/pricing modal which uses it as a fallback when no calendar is
configured. Open for discussion! -- May be we dont show the `Book a
Call` button if the env is not set -- but we should keep it as it is if
we want two different behaviors :)
  
  closes https://github.com/twentyhq/core-team-issues/issues/1558

packages/twenty-server/src/engine/core-modules/client-config/services/client-config.service.ts

@@ -1,5 +1,7 @@
 import { Injectable } from '@nestjs/common';
 
+import { isNonEmptyString } from '@sniptt/guards';
+
 import { NodeEnvironment } from 'src/engine/core-modules/twenty-config/interfaces/node-environment.interface';
 import { SupportDriver } from 'src/engine/core-modules/twenty-config/interfaces/support.interface';
 
@@ -28,6 +30,9 @@ export class ClientConfigService {
   async getClientConfig(): Promise<ClientConfig> {
     const captchaProvider = this.twentyConfigService.get('CAPTCHA_DRIVER');
     const supportDriver = this.twentyConfigService.get('SUPPORT_DRIVER');
+    const calendarBookingPageId = this.twentyConfigService.get(
+      'CALENDAR_BOOKING_PAGE_ID',
+    );
 
     const availableModels = this.aiModelRegistryService.getAvailableModels();
 
@@ -153,9 +158,9 @@ export class ClientConfigService {
       isImapSmtpCaldavEnabled: this.twentyConfigService.get(
         'IS_IMAP_SMTP_CALDAV_ENABLED',
       ),
-      calendarBookingPageId: this.twentyConfigService.get(
-        'CALENDAR_BOOKING_PAGE_ID',
-      ),
+      calendarBookingPageId: isNonEmptyString(calendarBookingPageId)
+        ? calendarBookingPageId
+        : undefined,
     };
 
     return clientConfig;

packages/twenty-server/src/engine/core-modules/onboarding/onboarding.service.ts

@@ -1,9 +1,12 @@
 import { Injectable } from '@nestjs/common';
 
+import { isNonEmptyString } from '@sniptt/guards';
+import { isDefined } from 'twenty-shared/utils';
 import { WorkspaceActivationStatus } from 'twenty-shared/workspace';
 
 import { BillingService } from 'src/engine/core-modules/billing/services/billing.service';
 import { OnboardingStatus } from 'src/engine/core-modules/onboarding/enums/onboarding-status.enum';
+import { TwentyConfigService } from 'src/engine/core-modules/twenty-config/twenty-config.service';
 import { UserVarsService } from 'src/engine/core-modules/user/user-vars/services/user-vars.service';
 import { type User } from 'src/engine/core-modules/user/user.entity';
 import { type Workspace } from 'src/engine/core-modules/workspace/workspace.entity';
@@ -27,6 +30,7 @@ export class OnboardingService {
   constructor(
     private readonly billingService: BillingService,
     private readonly userVarsService: UserVarsService<OnboardingKeyValueTypeMap>,
+    private readonly twentyConfigService: TwentyConfigService,
   ) {}
 
   private isWorkspaceActivationPending(workspace: Workspace) {
@@ -81,6 +85,22 @@ export class OnboardingService {
     }
 
     if (isBookOnboardingPending) {
+      const calendarBookingPageId = this.twentyConfigService.get(
+        'CALENDAR_BOOKING_PAGE_ID',
+      );
+      const isBookingConfigured =
+        isDefined(calendarBookingPageId) &&
+        isNonEmptyString(calendarBookingPageId);
+
+      if (!isBookingConfigured) {
+        await this.userVarsService.delete({
+          workspaceId: workspace.id,
+          key: OnboardingStepKeys.ONBOARDING_BOOK_ONBOARDING_PENDING,
+        });
+
+        return OnboardingStatus.COMPLETED;
+      }
+
       return OnboardingStatus.BOOK_ONBOARDING;
     }
 
@@ -171,7 +191,15 @@ export class OnboardingService {
     workspaceId: string;
     value: boolean;
   }) {
-    if (!value) {
+    const calendarBookingPageId = this.twentyConfigService.get(
+      'CALENDAR_BOOKING_PAGE_ID',
+    );
+
+    const isBookingConfigured =
+      isDefined(calendarBookingPageId) &&
+      isNonEmptyString(calendarBookingPageId);
+
+    if (!value || !isBookingConfigured) {
       await this.userVarsService.delete({
         workspaceId,
         key: OnboardingStepKeys.ONBOARDING_BOOK_ONBOARDING_PENDING,