[Copilot]

PNG files load successfully but fail later when decoded, potentially interrupting a running application. PNG encoding is also unavailable despite being documented as supported.

• Fail fast: Reject PNG files at load when the decoder is disabled.
• Protect files: Avoid truncating existing files when PNG encoding is unavailable.
• Cleanup: Release framebuffer allocations when image loading or saving raises an exception.
• Documentation: Clarify PNG availability in the bilingual guides and API stubs.

• Fixes [Firmware] image: PNG accepted at load but decode/save fail ("PNG decoder/encoder is not enabled") #23