refactor(header): modernize header styles and remove unused module

Update header component UI and streamline imports.

- Remove MatToolbarModule import and module list entry
  because the toolbar styling is handled by local SCSS and the
  Angular Material toolbar is no longer required.
- Rewrite header SCSS to introduce a .modern-header wrapper with
  consistent sizing, padding, alignment and a subtle bottom border.
- Add layered ambient and depth effects: refined ::before ambient
  gradient (headerAmbience), ::after bottom accent, and adjusted
  keyframes for a gentler motion.
- Refine home-header styles to target .modern-header and tune colors
  and gradients for a cohesive dark theme.
- Rework .brand-block visuals: lighter glass effect, adjusted
  radii, blur, borders, hover transform, and shadowing for a modern
  elevated look.
- Minor cleanup: remove legacy variables and comments; improve
  box-sizing, layout, and pointer-event handling to ensure expected
  interaction regions.

These changes modernize the header's visual design, improve layout
consistency across pages, and remove an unnecessary module import.

apps/web/src/app/shared/components/header/header.component.html

@@ -1,4 +1,4 @@
-<mat-toolbar class="modern-header">
+<div class="modern-header">
     <div class="brand-block">
         <div class="logo-pulse">
             <img
@@ -243,4 +243,4 @@
             </mat-menu>
         </div>
     }
-</mat-toolbar>
+</div>