feat(bookslm): v2.2.0 - BooksLM chat AI contextuel par répertoire + 4 providers AI

BooksLM (#76):
- Panneau chat slide-in 450px, clic-droit répertoire → 🧠 BooksLM
- Collecte récursive .md avec limites (200 fichiers, 200K chars)
- Cache SHA-256, redaction secrets, priorité README/index
- SSE streaming, badges sources cliquables, historique localStorage
- Commandes palette: BooksLM ouvrir/nouvelle conversation

Providers AI (4 nouveaux):
- NVIDIA (integrate.api.nvidia.com)
- QwenCloud (dashscope.aliyuncs.com)
- Xiaomi (api.xiaomi.com)
- Mistral (api.mistral.ai)
- Tous OpenAI-compatible, auto-listing modèles

Fix: dropdown config-select suit maintenant le thème (option bg/color)
27 tests BooksLM + 466 tests au total

frontend/locales/en.json

@@ -1546,5 +1546,23 @@
   "mfa.totp_code_label": "TOTP Code",
   "mfa.disable_confirm_btn": "Disable 2FA",
   "mfa.disabled_success": "2FA has been disabled.",
-  "mfa.fill_all_fields": "Please fill in all fields."
+  "mfa.fill_all_fields": "Please fill in all fields.",
+
+  "bookslm.title": "BooksLM",
+  "bookslm.files_indexed": "{count} files indexed",
+  "bookslm.chars_loaded": "{chars} chars loaded",
+  "bookslm.placeholder": "Ask a question about these documents...",
+  "bookslm.send": "Send",
+  "bookslm.new_conversation": "New conversation",
+  "bookslm.export": "Export conversation",
+  "bookslm.copy": "Copy",
+  "bookslm.regenerate": "Regenerate",
+  "bookslm.suggestion_summary": "Summarize this directory",
+  "bookslm.suggestion_themes": "What are the main themes?",
+  "bookslm.suggestion_contradictions": "Are there contradictions between these documents?",
+  "bookslm.no_context": "No files found in this directory",
+  "bookslm.context_too_large": "Directory too large — some files were truncated",
+  "bookslm.source": "Source",
+  "palette.bookslm_open": "BooksLM: Open for current directory",
+  "palette.bookslm_new": "BooksLM: New conversation"
 }