assets: unified tile render, empty-filter placeholder

* Orphaned items now use mediaTile() instead of a hand-written triple-
  ternary, so audio and PDF files render with the same icon/player tile
  as linked items. Eliminates the code duplication that caused audio
  files to fall through to the <img> path in the orphaned section.
* applyFilter() tracks visibleCount after toggling item display. When
  the active filter hides every item (e.g. "Audio" tab with no audio
  files) but total assets exist, a type-specific placeholder is shown:
  matching icon (ph-image / ph-music-note / ph-file-pdf) + "no {type}
  assets" text. Hidden again on the next filter switch that has results.
* Section header hide logic narrowed to [data-section]:not(.gallery-item)
  so it only targets the header divs, not the items themselves.

chore: bump version to 0.9.19

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

config.php

@@ -1,7 +1,7 @@
 <?php
 
 define('APP_NAME', 'hyprcrd');
-define('APP_VERSION', '0.9.18');
+define('APP_VERSION', '0.9.19');
 
 // Database path — writable directory, outside webroot
 define('DB_PATH', __DIR__ . '/data/hyprcrd.db');