feat: add Clear History button to delete all consumed instructions

- Backend: instruction_service.clear_consumed() bulk-deletes consumed rows
- Backend: DELETE /api/instructions/consumed route (preserves pending)
- Frontend: Clear button in consumed panel header (hidden when empty)
- Frontend: SSE handler for history.cleared event - instant UI update
- Frontend: api.clearConsumed() fetch wrapper

static/js/instructions.js

@@ -162,10 +162,11 @@ function renderConsumedCard(item) {
 // ── List renderers ────────────────────────────────────────────────────────
 
 export function initInstructions() {
-  const pendingList  = document.getElementById('pending-list');
-  const pendingBadge = document.getElementById('pending-badge');
-  const consumedList = document.getElementById('consumed-list');
-  const consumedBadge = document.getElementById('consumed-badge');
+  const pendingList    = document.getElementById('pending-list');
+  const pendingBadge   = document.getElementById('pending-badge');
+  const consumedList   = document.getElementById('consumed-list');
+  const consumedBadge  = document.getElementById('consumed-badge');
+  const clearHistoryBtn = document.getElementById('clear-history-btn');
 
   function render(instructions) {
     if (!instructions) return;
@@ -190,14 +191,30 @@ export function initInstructions() {
     consumedList.innerHTML = '';
     if (consumed.length === 0) {
       consumedList.innerHTML = `<div class="empty-state"><div class="empty-state__icon">◈</div>No consumed instructions yet</div>`;
+      clearHistoryBtn.style.display = 'none';
     } else {
       consumed.forEach(item => consumedList.appendChild(renderConsumedCard(item)));
+      clearHistoryBtn.style.display = '';
     }
     consumedBadge.textContent = consumed.length;
     consumedBadge.className   = `badge ${consumed.length > 0 ? 'badge--amber' : 'badge--muted'}`;
   }
 
   state.subscribe('instructions', render);
+
+  // Clear history button
+  clearHistoryBtn.addEventListener('click', async () => {
+    if (!confirm('Clear all consumed instruction history? This cannot be undone.')) return;
+    clearHistoryBtn.disabled = true;
+    try {
+      const res = await api.clearConsumed();
+      toast(`Cleared ${res.cleared} consumed instruction${res.cleared !== 1 ? 's' : ''}`, 'info');
+    } catch (e) {
+      toast(e.message, 'error');
+    } finally {
+      clearHistoryBtn.disabled = false;
+    }
+  });
 }
 
 // ── Composer ──────────────────────────────────────────────────────────────