chore: retire Bootstrap JS + tidy the dead index.php fallback

Nothing rendered uses Bootstrap's JS anymore (offcanvas → CSS :target;
carousels/tabs/tooltips → native per-page vanilla JS), so drop
'import * as bootstrap' + window.bootstrap from src/main.js. The bootstrap npm
package stays for the SCSS subset. v4-script bundle: 229 KB → 149 KB (-80 KB).

index.php was a 322-line fossil (old homepage with two dead BS carousels +
duplicated about/posts sections, even a stale themes/dw path) and is never
rendered — front-page.php owns '/', every other view has its own template.
Replace it with a minimal, correct posts-loop fallback (26 lines).

js/v4-script.min.js.LICENSE.txt

@@ -1,9 +1,3 @@
-/*!
-  * Bootstrap v5.3.8 (https://getbootstrap.com/)
-  * Copyright 2011-2025 The Bootstrap Authors (https://github.com/twbs/bootstrap/graphs/contributors)
-  * Licensed under MIT (https://github.com/twbs/bootstrap/blob/main/LICENSE)
-  */
-
 /*!
  * Lazy Load - jQuery plugin for lazy loading images
  *

src/main.js

@@ -9,8 +9,8 @@
 import $ from 'jquery';
 window.$ = window.jQuery = $;
 
-import * as bootstrap from 'bootstrap'; // also registers BS5 data-api (offcanvas, etc.)
-window.bootstrap = bootstrap;
+// Bootstrap JS retired: offcanvas → CSS :target, carousels/tabs/tooltips → native
+// per-page vanilla JS. The bootstrap npm package stays for the SCSS subset only.
 
 import Cookies from 'js-cookie';
 window.Cookies = Cookies;