Multi-device support, dynamic grid adaptation, keyboard action

- Multi-device: OpenAllDecks(), GET /api/decks, per-deck PageManagers
- Dynamic grid: frontend adapts to connected device layout
- Keyboard action: new action type for sending key combos via wtype/xdotool
- Key recorder UI: click-based modifier toggles + single key capture
- Config: remove hardcoded maxKey validation
- Screensaver and auto-switch sync across all decks

static/styles.css

@@ -107,7 +107,6 @@ main {
 
 .deck-grid {
   display: grid;
-  grid-template-columns: repeat(5, 1fr);
   gap: 8px;
   padding: 20px;
   background: var(--surface);
@@ -115,6 +114,33 @@ main {
   border: 1px solid var(--border);
 }
 
+.deck-selector {
+  display: flex;
+  gap: 4px;
+  margin-bottom: 8px;
+  align-self: stretch;
+}
+.deck-btn {
+  flex: 1;
+  padding: 6px 10px;
+  background: var(--bg);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-xs);
+  color: var(--text-muted);
+  font-size: 11px;
+  font-weight: 600;
+  font-family: inherit;
+  cursor: pointer;
+  transition: all var(--transition);
+  text-align: center;
+}
+.deck-btn:hover { color: var(--text); border-color: var(--border-light); }
+.deck-btn.active {
+  background: var(--accent);
+  color: #fff;
+  border-color: var(--accent);
+}
+
 .key-btn {
   aspect-ratio: 1;
   border: 1px solid var(--border);