VQkit v1.1 - VASP BAND EXPORT / WINDOWS UNICODE FIX

Problem fixed
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On Windows, a VASP band calculation with high-symmetry labels such as Γ could stop while writing VQkit_BANDS.dat. The locale-dependent default text encoding could reject the Unicode Γ character, leaving a file containing only the introductory header and Fermi energy. Because export happens before plotting, the band plot was then not produced.

Fixes
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1. VQkit_BANDS.dat is written explicitly as UTF-8.
2. VQkit_HIGH_SYMMETRY_ENERGIES.dat is written explicitly as UTF-8.
3. Band and k-point array dimensions are validated before export.
4. VQkit_BANDS.dat is first written to a temporary file and atomically replaced only after the complete table is successful.
5. A failed export no longer leaves a misleading header-only file.
6. Verified on the supplied graphene VASP EIGENVAL: 180 k-points, 16 bands, E_F = -3.4226 eV, Γ-M-K-Γ.
