fix(single): fill slide and video cover media like the image cover

Slide-mode images rendered at intrinsic ratio, top-aligned inside the
swiper chain (--pc-height:auto left .swiper-wrapper content-sized), so
the taller box showed a gap at the bottom and never center-cropped like
the image cover. The video cover had the same problem through
video-player.js (height:auto, capped at 70vh).

- aksrt_render_slider scale mode emits --pc-height/--m-height 100% so
  the wrapper/slide/img chain fills the ratio box and object-fit: cover
  center-crops inside it (same pattern as the .scale-height widgets)
- video-player.js renders the video at height:100% + object-fit:cover;
  with an undimensioned container height:100% degrades to auto,
  matching the previous behavior
- drop the dead .single-cover padding-bottom rules (every producer owns
  its height inline, and the rule squeezed the absolutely positioned
  slide inner) and the orphaned --single-cover-scale var in
  tokens.css/compat-vars.css/main.css/InlineStyleBuilder
- rebuild public bundles; extend the single-cover-height contract

src/Frontend/InlineStyleBuilder.php

@@ -76,7 +76,6 @@ class InlineStyleBuilder {
             '--font-heading'           => $font_stacks['ui'],
             '--aksrt-logo-width'       => $logo_width . 'px',
             '--nav-height'             => '60px',
-            '--single-cover-scale'     => '35%',
             '--posts-list-scale'       => (class_exists('\AKSRT\Settings\Settings') ? (\AKSRT\Settings\Settings::get_post_list_style_settings()['list_list_option']['scale'] ?? 70) : 70) . '%',
             '--posts-card-scale'       => (class_exists('\AKSRT\Settings\Settings') ? (\AKSRT\Settings\Settings::get_post_list_style_settings()['list_card_option']['scale'] ?? 70) : 70) . '%',
         ];