Add clear button and clearChat function

Added a clear button to the header and implemented the clearChat function to reset the chat.

static/index.html

@@ -547,6 +547,7 @@
     <div class="logo-icon">⚡</div>
     <div class="logo-text">Query<span>Mind</span></div>
     <div class="header-badge">
+      <button id="clear-btn" onclick="clearChat()" style="background:none;border:1px solid var(--border2);color:var(--muted);font-size:11px;padding:4px 10px;border-radius:5px;cursor:pointer;font-family:var(--mono);letter-spacing:0.5px;transition:all 0.15s;" onmouseover="this.style.borderColor='var(--danger)';this.style.color='#ff8fa3'" onmouseout="this.style.borderColor='var(--border2)';this.style.color='var(--muted)'">CLEAR</button>
       <span id="status-dot" class="status-dot"></span>
       <span id="status-label" class="badge">INITIALIZING</span>
     </div>
@@ -865,6 +866,14 @@
     if (el) el.remove();
   }
 
+  // ── Clear Chat
+  function clearChat() {
+    chat.innerHTML = '';
+    emptyState.style.display = '';
+    chat.appendChild(emptyState);
+    showToast('Chat cleared', 'success');
+  }
+
   // ── Escape HTML ───────────────────────────────────────────────
   function escapeHtml(str) {
     return String(str).replace(/&/g,'&amp;').replace(/</g,'&lt;').replace(/>/g,'&gt;').replace(/"/g,'&quot;');