fix(branding): unify hero logo SIZE the same way as visibility (#756)

Follow-on to the visibility fix in this PR — hero_logo_size had the same
split-brain: GalleryLayout read the global branding_logo_size live while
the hero-header path used the per-event snapshot, so a hero logo could
render at different sizes on different layouts and the global size didn't
reach hero-header galleries.

Now mirrored on the visibility model: NULL per-event hero_logo_size =
inherit branding_logo_size; explicit = override.

- Migration 153: hero_logo_size nullable + backfill NULL so existing
  galleries inherit the global size (restores GalleryLayout's prior
  live-global behaviour and fixes the hero-header staleness).
- Creation stores NULL unless explicit; gallery.js resolves
  per-event ?? global and sends the effective size.
- GalleryLayout now consumes that resolved size for the hero logo (new
  heroLogoSize prop) instead of the global — both render paths match.
- Admin size control gains a 'Use branding default' (inherit) option.

Verified: migration on SQLite + PG; live resolution (inherit follows
global both ways, override wins); creation stores NULL on PG; tsc clean,
106 adminEvents+gallery tests pass, build green.

backend/src/routes/adminEvents/crud.js

@@ -95,7 +95,7 @@ module.exports = (router) => {
     body('css_template_id').optional({ nullable: true, checkFalsy: true }).isInt(),
     // Hero logo settings
     body('hero_logo_visible').optional().isBoolean(),
-    body('hero_logo_size').optional().isIn(['small', 'medium', 'large', 'xlarge']),
+    body('hero_logo_size').optional({ nullable: true }).isIn(['small', 'medium', 'large', 'xlarge']),
     body('hero_logo_position').optional().isIn(['top', 'center', 'bottom']),
     // Header style settings (decoupled from layout)
     body('header_style').optional().isIn(['hero', 'standard', 'banner', 'minimal', 'none']),
@@ -346,7 +346,9 @@ module.exports = (router) => {
       const effectiveHeroLogoVisible = req.body.hero_logo_visible !== undefined
         ? formatBoolean(hero_logo_visible)
         : null;
-      const effectiveHeroLogoSize = req.body.hero_logo_size || brandingDefaults.hero_logo_size;
+      // NULL = inherit the global branding_logo_size (#756), resolved at read
+      // time. Only an explicit per-event size overrides it.
+      const effectiveHeroLogoSize = req.body.hero_logo_size || null;
       const effectiveHeroLogoPosition = req.body.hero_logo_position || brandingDefaults.hero_logo_position;
 
       // Inherit "Detect dev tools" from the global Image Security setting unless
@@ -1223,7 +1225,7 @@ module.exports = (router) => {
     body('css_template_id').optional({ nullable: true, checkFalsy: true }).isInt(),
     // Hero logo settings
     body('hero_logo_visible').optional().isBoolean(),
-    body('hero_logo_size').optional().isIn(['small', 'medium', 'large', 'xlarge']),
+    body('hero_logo_size').optional({ nullable: true }).isIn(['small', 'medium', 'large', 'xlarge']),
     body('hero_logo_position').optional().isIn(['top', 'center', 'bottom']),
     // Header style settings (decoupled from layout)
     body('header_style').optional().isIn(['hero', 'standard', 'banner', 'minimal', 'none']),

backend/src/routes/gallery.js

@@ -195,6 +195,7 @@ router.get('/:slug/info', async (req, res) => {
     
     const requiresPassword = !(event.require_password === false || event.require_password === 0 || event.require_password === '0');
     const globalHeroLogoVisible = await getAppSetting('branding_logo_display_hero', true);
+    const globalLogoSize = await getAppSetting('branding_logo_size', 'medium');
 
     res.json({
       event_name: event.event_name,
@@ -213,7 +214,8 @@ router.get('/:slug/info', async (req, res) => {
       enable_devtools_protection: event.enable_devtools_protection === true || event.enable_devtools_protection === 1 || event.enable_devtools_protection === '1',
       use_canvas_rendering: event.use_canvas_rendering === true || event.use_canvas_rendering === 1 || event.use_canvas_rendering === '1',
       hero_logo_visible: resolveHeroLogoVisible(event.hero_logo_visible, globalHeroLogoVisible),
-      hero_logo_size: event.hero_logo_size || 'medium',
+      // #756: NULL per-event size inherits the global branding_logo_size.
+      hero_logo_size: event.hero_logo_size || globalLogoSize || 'medium',
       hero_logo_position: event.hero_logo_position || 'top',
       hero_logo_url: event.hero_logo_url || null,
       header_style: event.header_style || 'standard',
@@ -649,6 +651,7 @@ router.get('/:slug/photos', verifyGalleryAccess, resolveGuest, async (req, res)
     // one switch controls both surfaces.
     const useOriginalFilenames = await getUseOriginalFilenames();
     const globalHeroLogoVisible = await getAppSetting('branding_logo_display_hero', true);
+    const globalLogoSize = await getAppSetting('branding_logo_size', 'medium');
 
     res.json({
       event: {
@@ -668,7 +671,7 @@ router.get('/:slug/photos', verifyGalleryAccess, resolveGuest, async (req, res)
         enable_devtools_protection: req.event.enable_devtools_protection === true,
         use_canvas_rendering: req.event.use_canvas_rendering === true,
         hero_logo_visible: resolveHeroLogoVisible(req.event.hero_logo_visible, globalHeroLogoVisible),
-        hero_logo_size: req.event.hero_logo_size || 'medium',
+        hero_logo_size: req.event.hero_logo_size || globalLogoSize || 'medium',
         hero_logo_position: req.event.hero_logo_position || 'top',
         hero_logo_url: req.event.hero_logo_url || null,
         header_style: req.event.header_style || 'standard',