FEAT: Plugins Manager - danh sach thu muc da muc (Add Directory + x xoa), scan phan loai rieng re VST/SoundFont theo dir

- Backend: plugin_dirs (list) thay vst_dir/soundfont_dir rieng — luu plugin_dirs.json, backward compat gop field cu; scan walk tung dir phan loai .vst3/.dll/.so -> vst_found, .sf2/.sf3 -> soundfonts (kem dir goc)
- SoundFontAutoScanner: system_sf_dirs (list) — scan tat ca thu muc user khai bao
- Frontend: PluginManagerModal — nut Add Directory (Tauri dialog / prompt fallback), moi dir co nut x xoa, nut Scan -> hien danh sach rieng re VST Instruments + SoundFonts (kem duong dan thu muc)
- Tests: +2 (save/get/scan phan loai, xoa dir)

tests/test_plugin_api.py

@@ -93,3 +93,55 @@ class TestPluginAPI:
             assert data["size_bytes"] == len(valid_content)
         elif resp.status_code == 403:
             pytest.skip("Permission denied for admin user")
+
+    def test_plugin_dirs_save_list(self):
+        """plugin_dirs (list) — save/get/effective + scan phân loại riêng rẽ."""
+        token = get_admin_token()
+        if not token:
+            pytest.skip("Cannot get admin token")
+        h = {"Authorization": f"Bearer {token}"}
+        import tempfile
+        with tempfile.TemporaryDirectory() as td:
+            # 2 dir giả: 1 chứa VST, 1 chứa SoundFont
+            vst_dir = os.path.join(td, "vsts")
+            sf_dir = os.path.join(td, "sfs")
+            os.makedirs(vst_dir)
+            os.makedirs(sf_dir)
+            open(os.path.join(vst_dir, "Synth1.vst3"), "w").write("x")
+            open(os.path.join(sf_dir, "piano.sf2"), "w").write("x")
+            # Save list
+            r = client.post("/api/v1/plugins/dirs", headers=h,
+                            json={"plugin_dirs": [vst_dir, sf_dir]})
+            assert r.status_code == 200
+            assert r.json()["plugin_dirs"] == [vst_dir, sf_dir]
+            # Get lại
+            g = client.get("/api/v1/plugins/dirs", headers=h)
+            assert g.json()["plugin_dirs"] == [vst_dir, sf_dir]
+            # Scan → phân loại riêng rẽ
+            s = client.post("/api/v1/plugins/scan", headers=h)
+            assert s.status_code == 200
+            data = s.json()
+            assert any(v["name"] == "Synth1" for v in data["vst_found"])
+            assert any(x["name"] == "piano" for x in data["soundfonts"])
+            assert data["vst_count"] == 1
+            assert data["soundfont_count"] == 1
+            # Mỗi entry có dir gốc
+            assert data["vst_found"][0]["dir"] == vst_dir
+            assert data["soundfonts"][0]["dir"] == sf_dir
+
+    def test_plugin_dirs_remove(self):
+        """Xóa 1 dir khỏi list → save lại → không còn trong effective."""
+        token = get_admin_token()
+        if not token:
+            pytest.skip("Cannot get admin token")
+        h = {"Authorization": f"Bearer {token}"}
+        import tempfile
+        with tempfile.TemporaryDirectory() as td:
+            d1 = os.path.join(td, "d1")
+            d2 = os.path.join(td, "d2")
+            os.makedirs(d1)
+            os.makedirs(d2)
+            client.post("/api/v1/plugins/dirs", headers=h, json={"plugin_dirs": [d1, d2]})
+            client.post("/api/v1/plugins/dirs", headers=h, json={"plugin_dirs": [d1]})
+            g = client.get("/api/v1/plugins/dirs", headers=h)
+            assert g.json()["plugin_dirs"] == [d1]