feat(ai): menu @ instantane, selecteurs agrandis et BooksLM racine (#82)

Nouvel endpoint GET /api/vault/{vault}/paths + prechargement et filtrage client du menu @ (affichage instantane des fichiers/repertoires). Selecteurs Fournisseur/Modele agrandis (0,8rem / 34px) pour s'aligner sur le reste du site. Ajout de BooksLM au menu contextuel de la racine des vaults.

tests/frontend/ai.test.mjs

@@ -1121,6 +1121,47 @@ async function main() {
     localStorage.clear();
   });
 
+  // ── 42c. Fast `@` menu: client-side filtering of the prefetched path index ──
+  await test("mention menu filters the prefetched path index instantly", async () => {
+    localStorage.clear();
+    const calls = [];
+    globalThis.fetch = async (url) => {
+      const u = String(url);
+      calls.push(u);
+      if (u.includes("/paths")) {
+        return {
+          ok: true, status: 200,
+          json: async () => ({ vault: "V", count: 3, results: [
+            { vault: "V", path: "notes/a.md", name: "a.md", type: "file" },
+            { vault: "V", path: "notes/b.md", name: "b.md", type: "file" },
+            { vault: "V", path: "projects", name: "projects", type: "directory" },
+          ] }),
+        };
+      }
+      return { ok: true, status: 200, json: async () => ({}) };
+    };
+    const b = new BooksLM();
+    b._panel = b._render();
+    document.body.appendChild(b._panel);
+    b._vault = "V";
+    await b._showMentionMenu("notes");
+    const menu = b._panel.querySelector(".bookslm-mention-menu");
+    assert.equal(menu.querySelectorAll(".bookslm-menu-item").length, 2, "client-side filter keeps notes/*");
+    assert.ok(!calls.some((u) => u.includes("/api/tree-search")), "no server search once the path cache is warm");
+    b._panel.remove();
+    localStorage.clear();
+  });
+
+  await test("vault root context menu exposes BooksLM", async () => {
+    const { readFileSync } = await import("node:fs");
+    const src = readFileSync(path.join(JS_DIR, "ui.js"), "utf-8");
+    const vaultBranch = src.slice(
+      src.indexOf("if (type === 'vault')"),
+      src.indexOf("} else if (type === 'directory')")
+    );
+    assert.ok(vaultBranch.includes("BooksLM"), "BooksLM entry present in the vault root context menu");
+  });
+
   // ── Summary ──
   console.log(`\n${passCount}/${testCount} tests passed`);
   if (passCount !== testCount) {

tests/test_api_main.py

@@ -312,6 +312,22 @@ class TestTreeSearch:
         data = resp.json()
         assert len(data["results"]) == 0
 
+    def test_vault_paths_returns_indexed_paths(self, client):
+        """Flat path index backs the AI assistant `@` mention menu."""
+        resp = client.get("/api/vault/TestVault/paths")
+        assert resp.status_code == 200
+        data = resp.json()
+        assert data["vault"] == "TestVault"
+        paths = [p["path"] for p in data["results"]]
+        assert "note1.md" in paths
+        assert all("type" in p for p in data["results"])
+
+    def test_vault_paths_rejects_unknown_vault(self, client):
+        resp = client.get("/api/vault/DoesNotExist/paths")
+        assert resp.status_code in (200, 403, 404)
+        if resp.status_code == 200:
+            assert resp.json()["results"] == []
+
 
 class TestSearchReplace:
     def test_search_replace_invalid(self, client):