Search toggle icon on mobile, 2-col desktop; update README badges

Search position:
- Desktop: 2 columns (16.667%), menu fills the rest
- Mobile: collapses to a magnifying glass icon button (like the
  hamburger) that expands the search form via Bootstrap collapse

README:
- Version moved to badge (03.09.04)
- Joomla badge updated to 5.x | 6.x
- PHP badge updated to 8.1+
- Removed inline VERSION from title

Remove obsolete build-release.sh and minify.js scripts (replaced
by CI workflow and PHP helper).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/index.php

@@ -448,7 +448,10 @@ $wa->useScript('user.js');         // js/user.js
 				</nav>
 			<?php endif; ?>
 			<?php if ($this->countModules('search', true)) : ?>
-				<div class="container-search">
+				<button class="search-toggler d-lg-none" type="button" data-bs-toggle="collapse" data-bs-target="#headerSearchCollapse" aria-controls="headerSearchCollapse" aria-expanded="false" aria-label="<?php echo Text::_('JSEARCH_FILTER_SUBMIT'); ?>">
+					<span class="fa-solid fa-magnifying-glass" aria-hidden="true"></span>
+				</button>
+				<div class="container-search collapse d-lg-block" id="headerSearchCollapse">
 					<jdoc:include type="modules" name="search" style="none" />
 				</div>
 			<?php endif; ?>