fix: keep active page on config save, add Cyrillic preview support, fix grid sizing

- daemon.go: save/restore active page on config reload instead of
  always activating default_page (fixes page switch on save)
- render.go: replace basicfont.Face7x13 with parseDisplayFace() for
  unicode/Cyrillic support in edit key preview
- web.go: add SSE endpoint (GET /api/events) for real-time page_changed
  events and POST /api/activate-page API
- app.js: persist active page via localStorage, listen for SSE
  page_changed events
- styles.css, index.html: fix grid sizing (width 100%, minmax(0, 1fr),
  aspect-ratio on key buttons, max-width 525px)

static/index.html

@@ -14,7 +14,7 @@
 
   <!-- ═══ Header ═══ -->
   <header>
-    <button class="icon-btn" @click="subView = 'switcher'" title="Switch page">
+    <button class="icon-btn" @click="view = 'grid'; subView = 'switcher'" title="Switch page">
       <i class="fas fa-layer-group"></i>
     </button>
 
@@ -53,7 +53,7 @@
           x-text="d.model + ' (' + d.keys_x + '\u00d7' + d.keys_y + ')'"></button>
       </template>
     </div>
-    <div class="deck-grid" :style="'grid-template-columns: repeat(' + activeDeck.keys_x + ', 1fr)'">
+    <div class="deck-grid" :style="'grid-template-columns: repeat(' + activeDeck.keys_x + ', minmax(0, 1fr))'">
       <template x-for="key in gridKeys" :key="key.index">
         <button class="key-btn"
           :style="key.displayBg ? { backgroundColor: key.displayBg } : {}"
@@ -68,7 +68,7 @@
           <span x-show="key.configured && !key.background && !key.icon && key.label"
             style="font-size:12px;color:#fff;opacity:0.75;text-align:center;line-height:1.2;padding:4px;"
             x-text="key.label"></span>
-          <span x-show="!key.configured" style="color:var(--text-muted);font-size:24px;opacity:0.5;">+</span>
+          <span x-show="!key.configured" style="color:var(--text-muted);font-size:24px;opacity:0.5;line-height:1;">+</span>
           <div class="action-icons" x-show="key.hasAction">
             <template x-for="(t, ti) in key.actionTypes.slice(0,3)" :key="ti">
               <i :class="'fas fa-' + actionIconMap[t] + ' action-icon type-' + t"