feat(ai): assistant AI multi-contexte + ergonomie sidebar et clavier

Contexte:
- Repertoire (mode historique BooksLM, via menu contextuel dossier)
- Documents (bouton flottant quand des documents sont ouverts)
- General (bouton flottant sans document: aide app + creation de fichiers)
- Le contexte est affiche dans le header; suggestions adaptees au mode
- Blocs obsigate-action rendus en carte avec bouton Appliquer (pas d'execution auto)

Backend:
- /api/ai/bookslm/context et /chat acceptent mode + context_files
- collect_files_context(), empty_context(), build_general_system_prompt()
- mode documents degrade vers general si aucun fichier lisible

Corrige:
- bouton flottant passait le chemin d'un fichier comme repertoire -> erreur
  'Aucun fichier markdown trouve dans ce dossier'
- panneau precedent masque (localStorage) ne se rouvrait plus
- selecteur fournisseur/modele deplace sur une ligne dediee (header actions visibles)
- Entree envoie, Ctrl+Entree insere un saut de ligne

Tests: test_bookslm.py (+13) et tests/frontend/ai.test.mjs (+8)

frontend/js/ai-fab.js

@@ -1,26 +1,14 @@
-// ObsiGate — Floating Action Button (FAB) to open/close the BooksLM AI sidebar.
-// Always visible in the bottom-right corner; hides while BooksLM is open.
+// ObsiGate — Floating Action Button (FAB) for the AI Assistant sidebar.
+// Always visible in the bottom-right corner; hides while the assistant panel
+// is expanded. Clicking it opens the assistant in the context that matches
+// the current application state (open documents, or General when none).
 import booksLM from './bookslm.js';
-import { state } from './state.js';
-import { showToast, TabManager } from './ui.js';
 import { t } from './i18n.js';
 import { safeCreateIcons } from './utils.js';
 
 let _fab = null;
 
-// Mirror palette.js getCurrentFile(): prefer the active tab, then fall back to state.
-function getCurrentFile() {
-  const id = TabManager._activeTabId;
-  if (id) {
-    const tab = TabManager._tabs.find((x) => x.id === id);
-    if (tab) return { vault: tab.vault, path: tab.path };
-  }
-  if (state.currentVault && state.currentPath) return { vault: state.currentVault, path: state.currentPath };
-  return null;
-}
-
-// The BooksLM panel is considered visible when it has `.open` without `.hidden`
-// (the header toggle collapses it off-screen via `.hidden`).
+// The panel is visible when it has `.open` without `.hidden`.
 function isBooksLmVisible() {
   const panel = document.querySelector('.bookslm-panel');
   return !!(panel && panel.classList.contains('open') && !panel.classList.contains('hidden'));
@@ -36,25 +24,14 @@ function syncVisibility() {
 }
 
 async function onClick() {
-  const f = getCurrentFile();
-  if (!f) {
-    showToast(t('toast.no_open_file'), 'error');
+  const panel = document.querySelector('.bookslm-panel');
+  // Collapsed panel: reveal it instead of reopening.
+  if (panel && panel.classList.contains('open') && panel.classList.contains('hidden')) {
+    booksLM._toggleSidebar();
     return;
   }
-
-  const sameDir = booksLM._isOpen && booksLM._vault === f.vault && booksLM._directory === f.path;
-  if (sameDir) {
-    // Already open for this directory: re-show a collapsed panel, or close it.
-    const panel = document.querySelector('.bookslm-panel');
-    if (panel && panel.classList.contains('hidden')) {
-      booksLM._toggleSidebar();
-    } else {
-      booksLM.close();
-    }
-    return;
-  }
-
-  await booksLM.open(f.vault, f.path);
+  // Otherwise open (or re-focus) the assistant for the current context.
+  await booksLM.openForCurrentContext();
 }
 
 export function initAIFab() {