fix: enable svelte a11y linting and fix violations

frontend/src/routes/portfolio/+page.svelte

@@ -727,6 +727,7 @@
 						{@const hasActiveFilters = Object.values(selectedFilters).some((v) => v && v !== '')}
 						{#if hasActiveFilters || selectedTag || selectedTags.length > 0}
 							<button
+								type="button"
 								class="filter-dropdown flex shrink-0 items-center justify-center"
 								onclick={clearFilters}
 								aria-label="Clear all filters"
@@ -750,6 +751,7 @@
 							{@const hasActiveFilter = selectedValue && selectedValue !== ''}
 							<div class="filter-dropdown relative shrink-0">
 								<button
+									type="button"
 									class="flex items-center gap-1 rounded-lg border border-gray-300 bg-white px-3 py-1.5 text-sm transition-colors hover:bg-gray-50 {hasActiveFilter
 										? 'border-primary bg-primary/10'
 										: ''}"
@@ -781,6 +783,7 @@
 							style="position: fixed; left: {dropdownPosition?.x}px; top: {dropdownPosition?.y}px;"
 						>
 							<button
+								type="button"
 								class="filter-dropdown flex w-full items-center justify-between px-3 py-2 text-left text-sm transition-colors hover:bg-fuchsia-50 {selectedValue ===
 								''
 									? 'bg-fuchsia-100 font-medium'
@@ -794,6 +797,7 @@
 							</button>
 							{#each filter.values as value (value.value)}
 								<button
+									type="button"
 									class="filter-dropdown flex w-full items-center justify-between px-3 py-2 text-left text-sm transition-colors hover:bg-fuchsia-50 {selectedValue ===
 									value.value
 										? 'bg-fuchsia-100 font-medium'
@@ -827,6 +831,7 @@
 
 				{#if selectedTag || selectedTags.length > 0}
 					<button
+						type="button"
 						class="flex shrink-0 items-center justify-center"
 						onclick={clearSearch}
 						aria-label="Clear search tags"
@@ -852,6 +857,7 @@
 	<div class="grid grid-cols-3 gap-1 p-2 pt-0 sm:grid-cols-4 md:grid-cols-6 lg:grid-cols-8">
 		{#each images as img (img.id)}
 			<button
+				type="button"
 				class="relative aspect-square overflow-hidden rounded-xs transition-opacity hover:opacity-90 active:opacity-75"
 				onclick={() => openModal(img)}
 				aria-label="View full size portfolio item"
@@ -970,6 +976,7 @@
 				</div>
 
 				<button
+					type="button"
 					bind:this={closeBtnRef}
 					class="absolute right-2 z-[60] rounded-full bg-black/50 p-2 text-white transition-colors hover:bg-black/70 sm:right-4"
 					onclick={closeModal}
@@ -987,6 +994,7 @@
 
 				{#if currentIndex > 0}
 					<button
+						type="button"
 						bind:this={prevButtonRef}
 						class="absolute top-1/2 left-2 z-[60] -translate-y-1/2 rounded-full bg-black/50 p-3 text-white transition-colors hover:bg-black/70 sm:left-4"
 						onclick={navigatePrev}
@@ -1005,6 +1013,7 @@
 
 				{#if currentIndex < images.length - 1}
 					<button
+						type="button"
 						bind:this={nextButtonRef}
 						class="absolute top-1/2 right-2 z-[60] -translate-y-1/2 rounded-full bg-black/50 p-3 text-white transition-colors hover:bg-black/70 sm:right-4"
 						onclick={navigateNext}