burn: add export/import save and keyboard shortcut help overlay (#47)

- Export button copies save JSON to clipboard
- Import button prompts for pasted save data, validates, and reloads
- Press ? to toggle hotkey overlay showing all keyboard shortcuts
- Press Escape to close the overlay
- Styling matches the existing cyber-monastic aesthetic

game.js

@@ -2131,6 +2131,65 @@ function saveGame() {
     showSaveToast();
 }
 
+
+// === EXPORT / IMPORT ===
+function exportSave() {
+    const raw = localStorage.getItem('the-beacon-v2');
+    if (!raw) { log('No save data to export.'); return; }
+    navigator.clipboard.writeText(raw).then(() => {
+        log('Save data copied to clipboard.');
+        showExportToast('Save copied to clipboard');
+    }).catch(() => {
+        // Fallback: select in a temporary textarea
+        const ta = document.createElement('textarea');
+        ta.value = raw;
+        document.body.appendChild(ta);
+        ta.select();
+        document.execCommand('copy');
+        document.body.removeChild(ta);
+        log('Save data copied to clipboard (fallback).');
+        showExportToast('Save copied to clipboard');
+    });
+}
+
+function importSave() {
+    const input = prompt('Paste save data:');
+    if (!input || !input.trim()) return;
+    try {
+        const data = JSON.parse(input.trim());
+        // Validate: must have expected keys
+        if (typeof data.code !== 'number' || typeof data.phase !== 'number') {
+            log('Invalid save data: missing required fields.');
+            return;
+        }
+        localStorage.setItem('the-beacon-v2', input.trim());
+        log('Save data imported. Reloading...');
+        showExportToast('Save imported — reloading');
+        setTimeout(() => location.reload(), 800);
+    } catch (e) {
+        log('Invalid save data: not valid JSON.');
+    }
+}
+
+function showExportToast(msg) {
+    const el = document.getElementById('save-toast');
+    if (!el) return;
+    el.textContent = msg;
+    el.style.display = 'block';
+    requestAnimationFrame(() => { el.style.opacity = '1'; });
+    setTimeout(() => {
+        el.style.opacity = '0';
+        setTimeout(() => { el.style.display = 'none'; }, 500);
+    }, 2000);
+}
+
+function toggleHotkeyHelp() {
+    const el = document.getElementById('hotkey-overlay');
+    if (!el) return;
+    el.style.display = el.style.display === 'flex' ? 'none' : 'flex';
+}
+
+
 function loadGame() {
     const raw = localStorage.getItem('the-beacon-v2');
     if (!raw) return false;
@@ -2308,4 +2367,12 @@ window.addEventListener('keydown', function (e) {
         else setBuyAmount(1);
     }
     if (e.code === 'KeyS') activateSprint();
+    if (e.code === 'Slash' && e.shiftKey) {
+        e.preventDefault();
+        toggleHotkeyHelp();
+    }
+    if (e.code === 'Escape') {
+        const el = document.getElementById('hotkey-overlay');
+        if (el) el.style.display = 'none';
+    }
 });