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- Remove the superseded logo_width plumbing: the setting (PHP + VUE schemas),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/Settings/DisplayPageGroups.php

@@ -149,7 +149,6 @@ trait DisplayPageGroups {
             'site_logo'                   => self::logo_url(),
             'site_logo_dark'              => self::logo_dark_url(),
             'logo_text'                   => self::logo_text(),
-            'logo_width'                  => self::logo_width(),
             'site_favicon'                => self::favicon_url(),
             'theme_mode'                  => self::theme_mode(),
             'theme_mode_button'           => self::get_theme_mode_button_positions(),