Refactor homepage and header components.

Moved header content logic based on `current_page` input for reusability. Updated styling and layout structure to improve maintainability and accommodate dynamic titles and subtitles.

frontend/src/app/header/header.component.ts

@@ -1,4 +1,5 @@
 import {Component, Input, OnInit} from '@angular/core';
+import {ALTITUDE_VERSION} from '../constant';
 
 @Component({
   standalone: false,
@@ -8,6 +9,7 @@ import {Component, Input, OnInit} from '@angular/core';
 })
 export class HeaderComponent implements OnInit {
   @Input() title: string = '';
+  @Input() sub_title: string = '';
   @Input() current_page: string = ''
 
   public ngOnInit(): void {
@@ -35,4 +37,5 @@ export class HeaderComponent implements OnInit {
     }
   }
 
+  protected readonly ALTITUDE_VERSION = ALTITUDE_VERSION;
 }