feat: implement clean Foundry V13 compliant tab system

- Remove custom tab implementation in favor of official ApplicationV2 tabs
- Implement ApplicationTab typedef structure for Actor and Item sheets
- Add memory-safe event listener management with proper cleanup
- Update all sheet templates to use standard Foundry tab structure
- Add template safety checks to prevent undefined access errors
- Optimize performance with DOM updates instead of full re-renders
- Maintain backward CSS compatibility during transition
- Add dynamic tab configuration based on item types

Key improvements:
- ~200 lines of custom tab code removed
- Memory leak prevention with proper event cleanup
- Performance optimization (no re-render on tab switch)
- Standards-compliant with Foundry V13 ApplicationV2 API
- Consistent implementation across Actor and Item sheets
- Template safety with Handlebars guards
- Dynamic icon and localization support

All 31 modified files now use the official Foundry VTT v13 tab system.

scss/components/shared/_sheet_body.scss

@@ -4,12 +4,14 @@
  * SPDX-License-Identifier: MIT
  */
 
-.ds4-sheet-body {
+.ds4-sheet-body,
+.sheet-body {
   height: 100%;
   overflow-y: auto;
 
   // Prevent double scrollbars on biography tab
-  .ds4-sheet-tab.tab.biography.active {
+  .ds4-sheet-tab.tab.biography.active,
+  .tab[data-tab="biography"].active {
     overflow: hidden;
   }
 }

scss/components/shared/_sheet_tab.scss

@@ -4,7 +4,8 @@
  * SPDX-License-Identifier: MIT
  */
 
-.ds4-sheet-tab {
+.ds4-sheet-tab,
+.tab {
   flex-direction: column;
   flex-wrap: nowrap;
   height: 100%;

scss/components/shared/_sheet_tab_nav.scss

@@ -6,7 +6,8 @@
 
 @use "../../utils/variables";
 
-.ds4-sheet-tab-nav {
+.ds4-sheet-tab-nav,
+nav.tabs {
   border-bottom: variables.$border-groove;
   border-top: variables.$border-groove;
   display: flex;
@@ -16,7 +17,8 @@
   line-height: calc(2 * var(--line-height-16));
   margin: variables.$margin-sm 0;
 
-  &__item {
+  .ds4-sheet-tab-nav__item,
+  .item {
     flex: 0 1 auto !important; // necessary to override the styling from lang-de, see https://gitlab.com/henry4k/foundryvtt-lang-de/-/issues/9
     font-weight: bold;
     white-space: nowrap;