feat(ai): section Fournisseur & modele compacte + correctifs menus @/ (#82, BUG-007, BUG-008)

Refonte de la section Fournisseur & modele de l'assistant : capacites regroupees dans une bulle d'information (survol/clic/appui long) au lieu d'une liste permanente, et liste de modeles avec recherche. Correctifs : detection Unicode + filtrage insensible aux accents des commandes / et mentions @, navigation clavier fiable, et prise en compte du contexte ad-hoc en mode General cote backend.

frontend/locales/en.json

@@ -128,6 +128,8 @@
   "ai.model_offline": "offline",
   "ai.model_load_error": "Load error",
   "ai.model_settings": "Provider & model",
+  "ai.model_search": "Search a model…",
+  "ai.model_info": "Model capabilities",
   "ai.add_context": "Add context",
   "ai.attach_image": "Attach an image",
   "ai.cap_audio_speech": "Audio Speech",
@@ -1269,7 +1271,7 @@
   "help.assistant_resize": "The left edge of the panel is resizable; the width is remembered.",
   "help.assistant_at": "Type @ to attach a file or directory to the context, or to attach an image from a directory.",
   "help.assistant_slash": "Type / to run a skill (research, summary, correction, plan…) or an admin command (/help, /providers, /model, /keys).",
-  "help.assistant_images": "Paste an image into the composer (or attach one) to analyse it with a vision-capable model; the selected model's capabilities are displayed.",
+  "help.assistant_images": "Paste an image into the composer (or attach one) to analyse it with a vision-capable model. The ⓘ button shows the selected model's capabilities, and the model list is filterable by search.",
   "help.toolbar_section": "AI toolbar",
   "help.tree_section": "Vault tree",
   "help.use_cases": "Use cases",