支持通过 UART 手动逐台添加相机再启动输出

保留已连接相机，添加失败不占用编号，并要求输出停止后才能新增。通过 23 项回归测试、真实 SDK 的 1–4 路逐台添加验证、Ruff 和文档检查。

tests/check_backend.py

@@ -55,9 +55,13 @@ def main():
     open_runtime = partial(FingerRuntime.open, map_cache=str(scratch / "uv-map.npz"))
     with patch.object(FingerRuntime, "open", side_effect=open_runtime):
         for count in range(1, 5):
-            bank = FingerSensorBank(sources[:count])
+            bank = FingerSensorBank()
             try:
-                bank.connect_all()
+                for source in sources[:count]:
+                    existing = dict(bank.runtimes)
+                    bank.add(source)
+                    assert all(bank.runtimes[i] is runtime for i, runtime in existing.items())
+                    assert len(bank.read_all()) == len(bank.runtimes)
                 runtimes = list(bank.runtimes.values())
                 for left, right in itertools.combinations(runtimes, 2):
                     assert left.capture is not right.capture
@@ -67,7 +71,7 @@ def main():
                     readings = bank.read_all()
                     assert [r.sensor_id for r in readings] == list(range(1, count + 1))
                     assert all(np.isfinite([r.normal, r.shear_x, r.shear_y]).all() for r in readings)
-                print(f"PASS {count} sources: independent captures/processors, 3 complete rounds", flush=True)
+                print(f"PASS {count} sources: incremental add/read, independent states, 3 final rounds", flush=True)
             finally:
                 bank.close()
             assert all(runtime.capture is None for runtime in runtimes)