fix(navigation): let CSS size the nav logo and drop the inline width cap

The navbar logo carried an inline `height:36px;width:auto;max-width:{logo_width}px`
while `.navbar-logo > img` already owns `height:36px;padding:0 30px`. Under
`box-sizing:border-box` that max-width capped the border box, so the 60px of
horizontal padding stayed inside it and wide logos were squeezed against a
fixed height, breaking the intrinsic aspect ratio.

- Render the nav logo with no inline sizing; CSS alone sizes it.
- Add a `$lazy` argument to jio_get_adaptive_theme_img() so the navbar can emit
  the real src up front instead of a square lazyload placeholder; defaults to
  'auto' so every other caller keeps the lazy_other behaviour.
- Remove the superseded logo_width plumbing: the setting (PHP + VUE schemas),
  Settings::logo_width(), jio_get_site_logo_width(), the --jio-logo-width token
  and the unused has_logo context key.
- Cover the contract in the header reference test.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/Admin/Schema/GlobalSchema.php

@@ -158,7 +158,6 @@ class GlobalSchema {
                         ['key' => 'logo', 'title' => 'Logo 设置', 'fields' => [
                             ['key' => 'site_logo', 'label' => '站点 Logo', 'type' => 'media', 'default' => ''],
                             ['key' => 'site_logo_dark', 'label' => '暗色模式 Logo', 'type' => 'media', 'default' => ''],
-                            ['key' => 'logo_width', 'label' => 'Logo 宽度', 'type' => 'number', 'default' => 150, 'min' => 50, 'max' => 400],
                             ['key' => 'logo_text', 'label' => 'Logo 文字', 'type' => 'input', 'default' => ''],
                         ]],
                         ['key' => 'favicon', 'title' => '站点图标', 'fields' => [