Adds authentication and pricing pages for user onboarding

Introduces comprehensive user authentication flow with plan selection and registration

Includes:
- Pricing page with plan details and selection
- Payment page with plan summary and card information
- Signup page for different plan tiers
- Shared authentication layout and design system improvements

Enhances user onboarding experience with clear plan information and streamlined signup process

PlanTempus.Application/wwwroot/css/sidebar.css

@@ -23,7 +23,7 @@ swp-side-menu {
 swp-side-menu-header {
   display: flex;
   align-items: center;
-  gap: 10px;
+  gap: var(--spacing-5);
   height: var(--topbar-height);
   padding: 0 var(--spacing-4);
   border-bottom: 1px solid var(--color-border);
@@ -100,7 +100,7 @@ a[is="swp-side-menu-item"] {
   display: flex;
   align-items: center;
   gap: var(--spacing-3);
-  padding: 10px var(--spacing-4);
+  padding: var(--spacing-5) var(--spacing-4);
   color: var(--color-text);
   cursor: pointer;
   transition: all var(--transition-fast);
@@ -146,7 +146,7 @@ swp-side-menu-action {
   align-items: center;
   justify-content: center;
   gap: var(--spacing-2);
-  padding: 10px;
+  padding: var(--spacing-5);
   font-size: var(--font-size-md);
   color: var(--color-text-secondary);
   background: transparent;