feat: add scale option to get command YAML config

[Copilot]

The get command lacked the scaling capability already available in export --scale-size. This adds a per-file scale field to the pepper-sprite.yaml config.

Changes

• FileConfig — new optional scale: String? field
• _parseConfig() — reads scale from each YAML file entry
• _processFile() — validates scale format (WIDTH,HEIGHT, positive integers, whitespace-tolerant) before download; logs error and marks file as failed on invalid input
• _exportFile() — accepts scaleWidth/scaleHeight and forwards them to ImageExporter.exportToPngFile()
• Tests — 4 new validation cases (non-numeric, single value, zero width, negative height)

Usage

files:
  - fileId: "ADasdQWEsd"
    output: "assets/images/buildings.png"
    scale: "512,512"

Invalid scale values cause that file to fail (counted in the error summary) without aborting remaining files.