Feature/onboarding slides (#4955)

# Description of Changes

- Added onboarding slides/upgrade banner conditions for all the
following cases
  - 'licensed'
  - 'no-login-user-under-limit-no-license'
  - 'no-login-admin-under-limit-no-license'
  - 'no-login-user-over-limit-no-license'
  - 'no-login-admin-over-limit-no-license'
  - 'login-user-under-limit-no-license'
  - 'login-admin-under-limit-no-license'
  - 'login-user-over-limit-no-license'
  - 'login-admin-over-limit-no-license';


---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

---------

Co-authored-by: Anthony Stirling <[email protected]>
Co-authored-by: Connor Yoh <[email protected]>

frontend/src/core/styles/theme.css

@@ -328,6 +328,19 @@
   --compare-page-label-fg: var(--text-secondary);
 }
 
+/* Onboarding (light mode) */
+:root {
+  --onboarding-title: #0A0A0A;
+  --onboarding-body: #4A5565;
+  --onboarding-primary-button-bg: #101828;
+  --onboarding-primary-button-text: #FFFFFF;
+  --onboarding-secondary-button-bg: #FFFFFF;
+  --onboarding-secondary-button-text: #6A7282;
+  --onboarding-secondary-button-border: #E5E5E5;
+  --onboarding-step-active: #1E2939;
+  --onboarding-step-inactive: #D1D5DC;
+}
+
 [data-mantine-color-scheme="dark"] {
   /* Dark theme gray scale (inverted) */
   --gray-50: 17 24 39;
@@ -548,6 +561,16 @@
   --modal-content-bg: #2A2F36;
   --modal-header-border: rgba(255, 255, 255, 0.08);
 
+  /* Onboarding (dark mode) */
+  --onboarding-title: #F9FAFB;
+  --onboarding-body: #D1D5DB;
+  --onboarding-primary-button-bg: #FFFFFF;
+  --onboarding-primary-button-text: #0B1220;
+  --onboarding-secondary-button-bg: transparent;
+  --onboarding-secondary-button-text: #E5E7EB;
+  --onboarding-secondary-button-border: #3A4047;
+  --onboarding-step-active: #E5E7EB;
+  --onboarding-step-inactive: #4B5563;
   /* API Keys section colors (dark mode) */
   --api-keys-card-bg: #2A2F36;
   --api-keys-card-border: #3A4047;