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/js/config.js

@@ -1343,7 +1343,7 @@ function updateRegexPreview() {
 async function loadAIKeys() {
   try {
     const data = await api("/api/config/ai-keys");
-    ["DEEPSEEK_API_KEY","OPENROUTER_API_KEY","GEMINI_API_KEY"].forEach(k => {
+    ["DEEPSEEK_API_KEY","OPENROUTER_API_KEY","GEMINI_API_KEY","NVIDIA_API_KEY","QWENCLOUD_API_KEY","XIAOMI_API_KEY","MISTRAL_API_KEY"].forEach(k => {
       const id = "cfg-" + k.toLowerCase().replace(/_api_key/g, "") + "-key";
       const input = document.getElementById(id);
       if (input && data[k]) input.placeholder = data[k];
@@ -1353,7 +1353,7 @@ async function loadAIKeys() {
 
 async function saveAIKeys() {
   const keys = {};
-  const map = { "cfg-deepseek-key": "DEEPSEEK_API_KEY", "cfg-openrouter-key": "OPENROUTER_API_KEY", "cfg-gemini-key": "GEMINI_API_KEY" };
+  const map = { "cfg-deepseek-key": "DEEPSEEK_API_KEY", "cfg-openrouter-key": "OPENROUTER_API_KEY", "cfg-gemini-key": "GEMINI_API_KEY", "cfg-nvidia-key": "NVIDIA_API_KEY", "cfg-qwencloud-key": "QWENCLOUD_API_KEY", "cfg-xiaomi-key": "XIAOMI_API_KEY", "cfg-mistral-key": "MISTRAL_API_KEY" };
   for (const [id, name] of Object.entries(map)) {
     const input = document.getElementById(id);
     if (input && input.value.trim()) keys[name] = input.value.trim();
@@ -1377,7 +1377,7 @@ async function testAIKeys() {
     var msg = Object.entries(results).map(([k,v]) => k + ": " + v).join(" | ");
     if (status) status.textContent = msg;
     // Fetch models for configured providers
-    for (const p of ["deepseek","openrouter","gemini"]) {
+    for (const p of ["deepseek","openrouter","gemini","nvidia","qwencloud","xiaomi","mistral"]) {
       if (results[p] === "ok") {
         try {
           const m = await api("/api/config/ai-models?provider=" + p);