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/app.js

@@ -10,6 +10,8 @@ document.addEventListener('alpine:init', () => {
     toast: null,
     displayOutputs: {},
     isCapturingKey: false,
+    decks: [],
+    activeDeckSerial: '',
 
     // ── Edit state ──
     editing: null,
@@ -25,9 +27,22 @@ document.addEventListener('alpine:init', () => {
     // ── Init ──
     async init() {
       await this.loadConfig()
+      await this.loadDecks()
       setInterval(() => this.pollDisplayOutputs(), 3000)
     },
 
+    async loadDecks() {
+      try {
+        const res = await fetch('/api/decks')
+        if (res.ok) {
+          this.decks = await res.json()
+          if (this.decks.length > 0 && !this.activeDeckSerial) {
+            this.activeDeckSerial = this.decks[0].serial
+          }
+        }
+      } catch (_) {}
+    },
+
     async pollDisplayOutputs() {
       if (this.view !== 'grid') return
       try {
@@ -69,12 +84,18 @@ document.addEventListener('alpine:init', () => {
       return this.pages.map(p => p.name)
     },
 
+    get activeDeck() {
+      return this.decks.find(d => d.serial === this.activeDeckSerial)
+        || { keys_x: 5, keys_y: 3, num_keys: 15 }
+    },
+
     // ── Grid ──
     get gridKeys() {
       const page = this.currentPage
       if (!page) return []
       const keys = []
-      for (let i = 0; i < 15; i++) {
+      const n = this.activeDeck.num_keys
+      for (let i = 0; i < n; i++) {
         const kc = page.keys.find(k => k.index === i)
         keys.push({
           index: i,