feat: add gzip toggle and cache mode (normal / no-cache / bust)

- Cache-mode selector: Normal, No-cache headers, Cache-bust URL+headers
- Cache-bust appends random ?_cb= per iteration to bypass CDN/proxy
- gzip toggle: on = k6 default (Accept-Encoding: gzip/br), off = identity
- Both options stored in DB with non-destructive migration
- History items show cache-mode and gzip pills
- Schema migration handles existing DBs gracefully

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/app.js

@@ -30,6 +30,15 @@ methodSel.addEventListener('change', () => {
   bodyGroup.style.display = (m !== 'GET' && m !== 'HEAD') ? '' : 'none';
 });
 
+// gzip toggle hint
+const gzipChk  = document.getElementById('gzip');
+const gzipHint = document.getElementById('gzip-hint');
+gzipChk.addEventListener('change', () => {
+  gzipHint.textContent = gzipChk.checked
+    ? 'k6 default — server may compress response'
+    : 'Sends Accept-Encoding: identity — forces uncompressed response';
+});
+
 // ---- Run Test ----
 const form      = document.getElementById('test-form');
 const startBtn  = document.getElementById('start-btn');
@@ -49,6 +58,8 @@ form.addEventListener('submit', async (e) => {
   const httpMethod  = document.getElementById('httpMethod').value;
   const requestBody = document.getElementById('requestBody').value.trim();
   const headers     = document.getElementById('headers').value.trim() || '{}';
+  const cacheMode   = document.getElementById('cacheMode').value;
+  const gzip        = document.getElementById('gzip').checked;
 
   // Validate headers JSON
   try { JSON.parse(headers); } catch {
@@ -69,7 +80,7 @@ form.addEventListener('submit', async (e) => {
     res = await fetch('/api/tests', {
       method: 'POST',
       headers: { 'Content-Type': 'application/json' },
-      body: JSON.stringify({ url, vus, duration, rpsLimit, httpMethod, requestBody, headers }),
+      body: JSON.stringify({ url, vus, duration, rpsLimit, httpMethod, requestBody, headers, cacheMode, gzip }),
     });
   } catch (err) {
     alert('Failed to start test: ' + err.message);
@@ -227,12 +238,22 @@ async function loadHistory() {
       summaryLine = parts.join(' · ');
     }
 
+    const cacheBadge = t.cache_mode === 'bust'
+      ? '<span class="pill bust">cache-bust</span>'
+      : t.cache_mode === 'no-cache'
+      ? '<span class="pill no-cache">no-cache</span>'
+      : '<span class="pill cached">cached</span>';
+    const gzipBadge = t.gzip
+      ? '<span class="pill gzip">gzip</span>'
+      : '<span class="pill no-gzip">no-gzip</span>';
+
     item.innerHTML = `
       <div>
         <div class="row1">
           <span class="badge ${t.status}">${t.status}</span>
           <span class="url">${escHtml(t.url)}</span>
           <span class="meta">${t.http_method} · ${t.vus} VUs · ${dur}</span>
+          ${cacheBadge}${gzipBadge}
         </div>
         <div class="meta">${date}</div>
         ${summaryLine ? `<div class="history-summary">${escHtml(summaryLine)}</div>` : ''}