feat(transcribe): UX improvements — progress bar, stats row, copy btn, char counter, batch errors

- Vocab textarea now shows live 0/500 char counter (turns amber at 450+)
- Animated progress bar during transcription; determinate for multi-clip, indeterminate for single
- Results card shows inline stats row (duration, language, speakers) and AI cleanup badge
- Copy button + Download TXT moved above transcript box; SRT/VTT remain below
- Speaker role legend repeats inside Segments panel for easy cross-reference
- Batch errors no longer halt the queue; remaining clips continue, failed files named in status bar

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

transcribe.php

@@ -45,7 +45,10 @@ require_once __DIR__ . '/includes/layout.php';
                             <button type="button" class="vocab-btn" data-preset="custom" data-i18n="vocabPresetCustom">Custom</button>
                         </div>
                         <textarea id="initPromptInput" name="initial_prompt" rows="2" placeholder="Technical terms and names for Whisper to recognise, e.g. Barnevernet, mediation, family services…" class="prompt-textarea" data-i18n-placeholder="vocabPlaceholder"></textarea>
-                        <p class="upload-hint" data-i18n="vocabHint">Helps Whisper recognise technical terms. Not included in the transcript.</p>
+                        <div class="vocab-footer">
+                            <p class="upload-hint" data-i18n="vocabHint">Helps Whisper recognise technical terms. Not included in the transcript.</p>
+                            <small class="control-hint vocab-char-count"><span id="vocabCharCount">0</span> / 500</small>
+                        </div>
                     </div>
 
                     <details id="advancedOptions" class="expert-field">