Convert OptimizationConfig from dataclass to Pydantic BaseModel with
field validators for ranges, types, and enum values. Missing/invalid
fields now produce actionable CLI errors instead of cryptic KeyErrors.
- Range validators: max_iterations>=1, minibatch_size>=1, seed>=0, etc.
- Enum validator: error_strategy must be skip|retry|abort
- Config migration hook via config_version field
- CLI catches ValidationError and prints per-field error messages
- Remove unused AppSettings class (Bug #7)
- 30 unit tests covering all validation edge cases
Co-Authored-By: Paperclip <noreply@paperclip.ing>