[Code scan] water.add_bonds fails assigning molecule IDs to hydrogens

Source: Codex global repository scan of deepmodeling/dpti at commit b719828e7eeb571bd26411430197cd74ea78e38c.
Project: https://github.com/orgs/deepmodeling/projects/27

Problem
`water.add_bonds()` assigns molecule IDs to hydrogen atoms with `mole_idx[ii] = mole_idx[bonds[ii]]`. For a normal hydrogen, `bonds[ii]` is a one-element list, so NumPy returns a one-element array. Assigning that array into a scalar slot raises `ValueError` with current NumPy.

Code references
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/lib/water.py#L68
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/lib/water.py#L158
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/lib/water.py#L165
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/lib/water.py#L166
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/hti_water.py#L242
https://github.com/deepmodeling/dpti/blob/b719828e7eeb571bd26411430197cd74ea78e38c/dpti/hti_water.py#L243

Reproduction
The CI-style test path currently reaches this through HTI water task generation:

```bash
cd tests
python -m unittest test_hti_water_gen_lammps_input.TestHtiWaterGenLammpsInput.test_hti_water_gen_old_json_gen_tasks
```

Observed result includes `ValueError: setting an array element with a sequence`.

Expected result
For H atoms, the code should use the bonded oxygen index, for example `bonds[ii][0]`, after validating that exactly one O-H owner was found.