Prepare TDSE page

[Faria22]

• Implement the TDSE prep page so the GUI mirrors the astraPrepareFiles_for_TDSE flow from the CLI,
  including loading existing settings from a user-selected ESSENTIAL_STATES_{label}.INP file (same
  behavior as pulse-file loading).
• Update copy in the UI: rename “TDSE calculation type” to “H spectrum type” and “Max photon energy”
  to “Max photoelectron energy”, while still displaying the ground-state energy for reference even when
  launching from an excited state.
• Allow the run to start either from a bound state (requiring state index and symmetry) or from a user-
  supplied wavefunction file; if no file is provided, fall back to the bound-state inputs.
• Expose a tolerance input that sets the acceptable wavefunction-norm variation before the propagator
  raises an error; typical values run between 1e-8 and 1e-6, with larger tolerances expected for complex
  H-spectrum runs.