ui: VOD list filter with persistence + Ctrl+F focus + Esc clear

Filter row above the VOD grid lets the user search the loaded archive
by title. Concrete user pain: streamers commonly have hundreds of VODs
and the current UI only supported scrolling.

- vodFilterInput / vodFilterClearBtn / vodFilterCount in index.html
- localized placeholder + clear-button title (DE + EN)
- vodFilterQuery state persisted to localStorage as
  twitch-vod-manager:vod-filter so the search bar survives reloads
- renderVODs split: it now caches lastLoadedVods + lastLoadedStreamer
  and delegates to renderVodGridFromCurrentState which applies
  filterVodsByQuery on every input event (no re-fetch)
- empty-state DOM is now built with createElement + textContent (via
  setVodGridEmptyState) instead of an innerHTML template, even for
  locale-only strings — defence in depth
- keyboard: Ctrl/Cmd+F focuses the filter when the VODs tab is active
  (Electron has no native find bar, so the default is suppressed). Esc
  clears the filter when the input has focus and content. Esc still
  closes modals first if any are open.

docs/IMPROVEMENT_LOG.md: Cycle 3 dated section.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/index.html

@@ -239,6 +239,11 @@
             <div class="content">
                 <!-- VODs Tab -->
                 <div class="tab-content active" id="vodsTab">
+                    <div class="vod-filter-row" style="display:flex; align-items:center; gap:8px; margin-bottom:12px;">
+                        <input type="text" id="vodFilterInput" placeholder="Filter VODs..." oninput="onVodFilterInput()" style="flex:1; background: var(--bg-secondary,#222); border:1px solid var(--border-color,#444); border-radius:6px; padding:8px 12px; color: var(--text-primary,#fff); font-size:13px;">
+                        <button id="vodFilterClearBtn" onclick="clearVodFilter()" title="Clear filter" style="display:none; background:transparent; border:1px solid var(--border-color,#444); border-radius:6px; padding:8px 12px; color: var(--text-secondary,#888); cursor:pointer;">x</button>
+                        <span id="vodFilterCount" style="color: var(--text-secondary,#888); font-size:12px; min-width:80px;"></span>
+                    </div>
                     <div class="vod-grid" id="vodGrid">
                         <div class="empty-state">
                             <svg viewBox="0 0 24 24" fill="currentColor"><path d="M21 3H3c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h18c1.1 0 2-.9 2-2V5c0-1.1-.9-2-2-2zm-9 14l-5-4 5-4v8zm2-8l5 4-5 4V9z"/></svg>