feat(frontend): redesign homepage and file config form with aurora palette

Rebuild the visual identity from the actual Ombrora mark (violet/cyan aurora
blobs) instead of the generic blue/amber scheme, add Bricolage Grotesque and
IBM Plex Mono for display and code-like text, and give the hero an animated
aurora backdrop, gradient headline, and a format-pair marquee driven by the
real registered converters.

Rework the file config form: target format and icon size are both chip
groups now instead of a native select, and quality/compression sliders get a
gradient-filled track, custom thumb, and a mono value pill to match. File
type icons are color-coded by family (images/documents/fonts/ebooks) and
reused across FileConfigCard, FileCard, and FormatsGrid.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/locales/en.json

@@ -7,6 +7,7 @@
     "themeToDark": "Switch to dark mode"
   },
   "hero": {
+    "kicker": "Drop. Convert. Done.",
     "title": "Convert your files online, for free",
     "subtitle": "Drag and drop your files, pick the output format, download the result. No install, no account.",
     "dropzoneLabel": "Drag your files here or click to browse",
@@ -14,8 +15,9 @@
     "unsupportedFormat": "Unsupported format"
   },
   "quality": {
-    "label": "Quality ({{value}})",
-    "compression": "Compression ({{value}})",
+    "targetFormat": "Convert to",
+    "label": "Quality",
+    "compression": "Compression",
     "iconSize": "Icon size",
     "compressPdf": "Compress as JPEG"
   },
@@ -25,10 +27,10 @@
   },
   "reassurance": {
     "title": "Why you can trust us",
-    "autoDelete": "Files deleted automatically after 1h",
+    "autoDelete": "Files deleted automatically after {{value}}h",
     "noAccount": "No account required",
     "online": "100% online — nothing to install",
-    "maxSize": "Up to 100MB per file"
+    "maxSize": "Up to {{value}}MB per file"
   },
   "formats": {
     "title": "Supported formats",

frontend/src/locales/fr.json

@@ -7,6 +7,7 @@
     "themeToDark": "Activer le mode sombre"
   },
   "hero": {
+    "kicker": "Glissez. Convertissez. Terminé.",
     "title": "Convertissez vos fichiers en ligne, gratuitement",
     "subtitle": "Glissez-déposez vos fichiers, choisissez le format de sortie, téléchargez le résultat. Aucune installation, aucun compte.",
     "dropzoneLabel": "Glissez vos fichiers ici ou cliquez pour parcourir",
@@ -14,8 +15,9 @@
     "unsupportedFormat": "Format non supporté"
   },
   "quality": {
-    "label": "Qualité ({{value}})",
-    "compression": "Compression ({{value}})",
+    "targetFormat": "Convertir en",
+    "label": "Qualité",
+    "compression": "Compression",
     "iconSize": "Taille de l'icône",
     "compressPdf": "Compresser en JPEG"
   },
@@ -25,10 +27,10 @@
   },
   "reassurance": {
     "title": "Pourquoi nous faire confiance",
-    "autoDelete": "Fichiers supprimés automatiquement après 1h",
+    "autoDelete": "Fichiers supprimés automatiquement après {{value}}h",
     "noAccount": "Aucun compte requis",
     "online": "100% en ligne — rien à installer",
-    "maxSize": "Jusqu'à 100 Mo par fichier"
+    "maxSize": "Jusqu'à {{value}} Mo par fichier"
   },
   "formats": {
     "title": "Formats pris en charge",