feat(contacts): revamp edit dialog with live preview + avatar picker

Rebuild the add/edit contact dialog on the portfolio-editor design language:

- A live preview card at the top shows the contact exactly as it renders in the
  list (avatar + name + address), updating as you type and pick an avatar.
- An avatar picker (Badge / Icon / Image segmented control) lets you keep the
  default Z/T type badge, choose a Material wallet icon from a searchable grid,
  or set a custom image. The picker area is fixed-height so the modal doesn't
  jump when switching modes.
- Custom images go through a new in-app ImagePicker (image_picker.h): a
  Material overlay that browses the filesystem starting at the user's Pictures
  folder, shows a thumbnail grid (decoded to raw pixels, box-downscaled to a
  small texture, cached per directory and freed on navigate/close, budgeted a
  few decodes per frame so large folders don't hitch), and returns the chosen
  path. The chosen image is copied into <config>/contact-avatars/ (named by an
  FNV hash of the source path, so re-picking is idempotent) and stored as
  "img:<path>". Like FolderPicker, it takes over the modal surface while open.
- Paste is now available on both add and edit; buttons are content-sized.

Adds three sweep surfaces (contacts-edit-{icon,badge,image}) that open the
dialog on a seeded contact in each avatar mode, plus i18n keys (+ 8-language
translations; reworded two zh/ja strings to stay within the existing CJK
subset, so no font rebuild).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

res/lang/fr.json

@@ -287,9 +287,20 @@
     "console_welcome": "Bienvenue dans la console ObsidianDragon",
     "console_zoom_in": "Agrandir",
     "console_zoom_out": "Réduire",
+    "contact_avatar": "AVATAR",
+    "contact_avatar_badge": "Badge",
+    "contact_avatar_badge_hint": "Utilise le badge de type d'adresse — Z pour blindée, T pour transparente.",
+    "contact_avatar_choose": "Choisir une image…",
+    "contact_avatar_copy_failed": "Impossible de copier cette image.",
+    "contact_avatar_icon": "Icône",
+    "contact_avatar_image": "Image",
+    "contact_avatar_image_hint": "L'image est copiée dans l'application pour rester disponible si l'original est déplacé.",
+    "contact_avatar_remove": "Retirer",
     "contact_global": "Afficher dans tous les portefeuilles (contact global)",
     "contact_global_badge_tt": "Contact global — visible dans tous les portefeuilles",
     "contact_global_tt": "Activé : ce contact reste visible quel que soit le portefeuille chargé. Désactivé : il appartient au portefeuille actuel uniquement.",
+    "contact_preview_addr": "L'adresse apparaîtra ici",
+    "contact_preview_name": "Nom du contact",
     "contacts": "Contacts",
     "contacts_search_no_match": "Aucun contact correspondant",
     "contacts_search_placeholder": "Rechercher des contacts...",
@@ -465,6 +476,12 @@
     "hide_qr": "Masquer le QR",
     "hide_zero_balances": "Masquer les soldes à 0",
     "history": "Historique",
+    "img_picker_count": "%d image(s) dans ce dossier",
+    "img_picker_empty": "Ce dossier ne contient ni sous-dossiers ni images.",
+    "img_picker_none": "Aucune image dans ce dossier",
+    "img_picker_pictures": "Dossier Images",
+    "img_picker_title": "Choisir une image",
+    "img_picker_use": "Utiliser l'image",
     "immature_type": "Immature",
     "import": "Importer",
     "import_key_address": "Adresse :",