feat(tenant): per-theme logos + file-upload + button UI polish

Replace the single tenant avatar with a pair of theme-scoped brand logos.
Render only the theme-matching <img> server-side and swap src on theme
toggle via a JS hook — no reload, no double request, no CSS tricks.

Tenant logos
- TenantLogoService (ImageUploadTrait) with theme whitelist and per-theme
  storage storage/tenants/{uuid}/logo/{light|dark}/, SIZES 128/256/512
- Public serving endpoint auth/tenant-logo-file so login can show the
  logo pre-auth; matching authenticated admin preview endpoint
- appTenantLogoUrl(?size, ?theme) with 4-step fallback cascade; PDF +
  mail always request 'light'
- Admin tenant edit: avatar block replaced by "Tenant logos" details
  block inside the Master-data tab, two side-by-side slots via Pico
  .grid with the core app-file-upload partial
- Policy rename ABILITY_ADMIN_TENANTS_AVATAR_VIEW -> LOGO_VIEW, action
  routes logo / logo-delete / logo-file with theme body/query param
- API endpoint path kept (backward compat), internals on new service
- CLI tenant:logo-migrate-avatars moves legacy avatar/ -> logo/light/
  idempotently (--dry-run, --yes, --cleanup)
- i18n "Tenant image" removed, 12 new keys synced across de/en

File upload component
- Full-width preview + filename/actions below (3D stack layout)
- Fixed 16:9 aspect ratio with 1rem inner padding for consistent
  preview size across any logo aspect
- Transparency checker pattern as background so black logos stay
  visible on dark mode and white logos on light mode
- form="" + deleteFormId support so the partial works with barrier
  forms inside another form

Buttons
- width:100% dropped from button[type="submit"]; scoped back via
  .login-main for the auth-flow primary CTA
- .outline base rule now tints background via color-mix of --app-color
  so secondary/primary/danger outlines all gain a subtle surface
- .outline.secondary restyled Stripe-style in both themes: solid white
  chip with soft shadow in light, solid elevated dark chip with white
  text in dark; neutral border replaces role-colored border
- .app-action-success/.app-action-danger outlines get color-mix bg +
  theme-aware outline-text tokens for stronger contrast
- Filled .primary/.app-action-success/.app-action-danger get raised
  box-shadow (inset highlight + drop) — opt-in via class so chrome
  buttons stay flat
- Dropped the legacy .secondary utility that was clobbering the
  custom-property cascade with a hardcoded muted color

Theme swap
- Logo img carries data-src-light + data-src-dark; theme-toggle JS
  swaps src when data-theme changes, keeping the topbar/login logo in
  sync without a page reload

Quality gates: PHPUnit (2045), PHPStan L5, CS-Fixer, docs link/drift,
codex skills sync — all green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

i18n/default_de.json

@@ -322,6 +322,18 @@
   "Upload logo": "Logo hochladen",
   "Logo updated": "Logo aktualisiert",
   "Logo removed": "Logo entfernt",
+  "Tenant logos": "Mandanten-Logos",
+  "Light logo": "Logo (hell)",
+  "Dark logo": "Logo (dunkel)",
+  "Upload light logo": "Helles Logo hochladen",
+  "Upload dark logo": "Dunkles Logo hochladen",
+  "Delete light logo": "Helles Logo löschen",
+  "Delete dark logo": "Dunkles Logo löschen",
+  "No logo for this theme yet": "Für dieses Theme wurde noch kein Logo hochgeladen",
+  "Delete this logo?": "Dieses Logo löschen?",
+  "Invalid theme": "Ungültiges Theme",
+  "Logo": "Logo",
+  "Remove": "Entfernen",
   "Allowed file types: SVG, PNG, JPG, WEBP": "Erlaubte Dateitypen: SVG, PNG, JPG, WEBP",
   "Favicon": "Favicon",
   "Upload favicon": "Favicon hochladen",
@@ -462,7 +474,6 @@
   "Tenant can not be deleted while departments are assigned": "Mandant kann nicht gelöscht werden, solange Abteilungen zugewiesen sind",
   "Tenant can not be created": "Mandant kann nicht erstellt werden",
   "Tenant can not be updated": "Mandant kann nicht aktualisiert werden",
-  "Tenant image": "Mandantenbild",
   "Assigned tenants": "Zugewiesene Mandanten",
   "Assigned tenant": "Zugewiesener Mandant",
   "Primary tenant": "Hauptmandant",

i18n/default_en.json

@@ -322,6 +322,18 @@
   "Upload logo": "Upload logo",
   "Logo updated": "Logo updated",
   "Logo removed": "Logo removed",
+  "Tenant logos": "Tenant logos",
+  "Light logo": "Light logo",
+  "Dark logo": "Dark logo",
+  "Upload light logo": "Upload light logo",
+  "Upload dark logo": "Upload dark logo",
+  "Delete light logo": "Delete light logo",
+  "Delete dark logo": "Delete dark logo",
+  "No logo for this theme yet": "No logo for this theme yet",
+  "Delete this logo?": "Delete this logo?",
+  "Invalid theme": "Invalid theme",
+  "Logo": "Logo",
+  "Remove": "Remove",
   "Allowed file types: SVG, PNG, JPG, WEBP": "Allowed file types: SVG, PNG, JPG, WEBP",
   "Favicon": "Favicon",
   "Upload favicon": "Upload favicon",
@@ -462,7 +474,6 @@
   "Tenant can not be deleted while departments are assigned": "Tenant can not be deleted while departments are assigned",
   "Tenant can not be created": "Tenant can not be created",
   "Tenant can not be updated": "Tenant can not be updated",
-  "Tenant image": "Tenant image",
   "Assigned tenants": "Assigned tenants",
   "Assigned tenant": "Assigned tenant",
   "Primary tenant": "Primary tenant",