Improve layout/behavior and accessibility

hdyc-svelte/src/lib/components/Calculator.svelte

@@ -75,7 +75,13 @@
 
     {#if !has3}
       <div class="swap-col">
-        <button class="swap-btn" on:click={swap} title="Swap values">
+        <button
+          type="button"
+          class="swap-btn"
+          on:click={swap}
+          title="Swap values"
+          aria-label="Swap conversion direction"
+        >
           <svg width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
             <path d="M7 16l-4-4 4-4M17 8l4 4-4 4M3 12h18" />
           </svg>
@@ -111,7 +117,9 @@
   </div>
 
   <div class="calc-footer">
-    <button class="clear-btn" on:click={clear}>Clear</button>
+    <button type="button" class="clear-btn" on:click={clear} aria-label="Clear calculator inputs">
+      Clear
+    </button>
     {#if config.factor && config.type === 'standard'}
       <span class="formula-hint">
         1 {config.labels.in1} = {config.factor}{config.offset ? ` + ${config.offset}` : ''} {config.labels.in2}