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)

tests/test_bookslm.py

@@ -574,3 +574,175 @@ class TestBooksLMChatEndpoint:
         finally:
             import shutil
             shutil.rmtree(sub, ignore_errors=True)
+
+
+# ── Unit tests: explicit documents context + general prompt ────────────
+
+
+class TestCollectFilesContext:
+    """Tests for collect_files_context() (Documents mode)."""
+
+    def test_collects_only_requested_files(self, tmp_path):
+        from backend.bookslm import collect_files_context
+
+        vault = tmp_path / "vault"
+        (vault / "sub").mkdir(parents=True)
+        (vault / "a.md").write_text("# A", encoding="utf-8")
+        (vault / "b.md").write_text("# B", encoding="utf-8")
+        (vault / "sub" / "c.md").write_text("# C", encoding="utf-8")
+
+        result = collect_files_context(vault, ["a.md", "sub/c.md"], scope="documents")
+
+        assert result["scope"] == "documents"
+        assert result["file_count"] == 2
+        assert [f["path"] for f in result["files"]] == ["a.md", "sub/c.md"]
+        assert result["directory_tree"] == ""
+
+    def test_ignores_paths_outside_vault(self, tmp_path):
+        from backend.bookslm import collect_files_context
+
+        vault = tmp_path / "vault"
+        vault.mkdir()
+        (vault / "ok.md").write_text("# ok", encoding="utf-8")
+        outside = tmp_path / "outside.md"
+        outside.write_text("# secret", encoding="utf-8")
+
+        result = collect_files_context(vault, ["../outside.md", "ok.md"])
+
+        assert result["file_count"] == 1
+        assert result["files"][0]["path"] == "ok.md"
+
+    def test_deduplicates_paths(self, tmp_path):
+        from backend.bookslm import collect_files_context
+
+        vault = tmp_path / "vault"
+        vault.mkdir()
+        (vault / "dup.md").write_text("# dup", encoding="utf-8")
+
+        result = collect_files_context(vault, ["dup.md", "dup.md"])
+
+        assert result["file_count"] == 1
+
+    def test_empty_context(self):
+        from backend.bookslm import empty_context
+
+        ctx = empty_context("general")
+        assert ctx["file_count"] == 0
+        assert ctx["files"] == []
+        assert ctx["scope"] == "general"
+
+
+class TestGeneralPrompt:
+    def test_general_prompt_lists_vaults(self):
+        from backend.bookslm import build_general_system_prompt
+
+        prompt = build_general_system_prompt(["Alpha", "Beta"])
+        assert "Alpha" in prompt
+        assert "Beta" in prompt
+        assert "obsigate-action" in prompt
+
+    def test_documents_prompt_scope(self):
+        from backend.bookslm import build_system_prompt
+
+        context = {
+            "files": [{"path": "a.md", "title": "A", "content": "hello"}],
+            "file_count": 1,
+            "total_chars": 5,
+            "directory_tree": "",
+        }
+        prompt = build_system_prompt(context, scope="documents")
+        assert "Documents ouverts" in prompt
+        assert "hello" in prompt
+
+
+class TestBooksLMContextModes:
+    """Tests for the mode-aware /context endpoint."""
+
+    def test_general_mode_needs_no_vault(self, bookslm_client):
+        token, _ = _login_bookslm(bookslm_client)
+        resp = bookslm_client.post(
+            "/api/ai/bookslm/context",
+            json={"mode": "general"},
+            headers={"Authorization": f"Bearer {token}"},
+        )
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["scope"] == "general"
+        assert data["file_count"] == 0
+        assert data["files"] == []
+
+    def test_documents_mode_returns_selected_files(self, bookslm_client):
+        token, _ = _login_bookslm(bookslm_client)
+        resp = bookslm_client.post(
+            "/api/ai/bookslm/context",
+            json={
+                "mode": "documents",
+                "vault": "TestVault",
+                "context_files": ["notes/note1.md"],
+            },
+            headers={"Authorization": f"Bearer {token}"},
+        )
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["scope"] == "documents"
+        assert data["file_count"] == 1
+        assert data["files"][0]["path"] == "notes/note1.md"
+
+    def test_documents_mode_without_files_degrades_to_general(self, bookslm_client):
+        token, _ = _login_bookslm(bookslm_client)
+        resp = bookslm_client.post(
+            "/api/ai/bookslm/context",
+            json={"mode": "documents", "vault": "TestVault", "context_files": []},
+            headers={"Authorization": f"Bearer {token}"},
+        )
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["scope"] == "general"
+        assert data["file_count"] == 0
+
+    def test_documents_mode_requires_vault(self, bookslm_client):
+        token, _ = _login_bookslm(bookslm_client)
+        resp = bookslm_client.post(
+            "/api/ai/bookslm/context",
+            json={"mode": "documents", "context_files": ["notes/note1.md"]},
+            headers={"Authorization": f"Bearer {token}"},
+        )
+        assert resp.status_code == 400
+
+    def test_unknown_mode_falls_back_to_directory(self, bookslm_client):
+        token, _ = _login_bookslm(bookslm_client)
+        resp = bookslm_client.post(
+            "/api/ai/bookslm/context",
+            json={"mode": "bogus", "vault": "TestVault", "directory": "notes"},
+            headers={"Authorization": f"Bearer {token}"},
+        )
+        assert resp.status_code == 200
+        assert resp.json()["scope"] == "directory"
+
+
+class TestBooksLMChatModes:
+    def test_general_chat_does_not_require_vault(self, bookslm_client):
+        """General mode must not 400/404 on a missing vault (only 500 if no key)."""
+        token, _ = _login_bookslm(bookslm_client)
+        resp = bookslm_client.post(
+            "/api/ai/bookslm/chat",
+            json={"mode": "general", "message": "Bonjour"},
+            headers={"Authorization": f"Bearer {token}"},
+        )
+        assert resp.status_code in (200, 500), f"unexpected {resp.status_code}: {resp.text[:200]}"
+        assert resp.status_code != 422
+
+    def test_documents_chat_accepts_context_files(self, bookslm_client):
+        token, _ = _login_bookslm(bookslm_client)
+        resp = bookslm_client.post(
+            "/api/ai/bookslm/chat",
+            json={
+                "mode": "documents",
+                "vault": "TestVault",
+                "context_files": ["notes/note1.md"],
+                "message": "Résume",
+            },
+            headers={"Authorization": f"Bearer {token}"},
+        )
+        assert resp.status_code in (200, 500), f"unexpected {resp.status_code}: {resp.text[:200]}"
+        assert resp.status_code != 422