Asset Manager 0.0.3

Draft built from 02fa5df by the release workflow. Check it against
the clean-machine list in docs/releasing.md before publishing.

Portable builds (*_portable.tar.gz, *_portable.zip) keep their data
in AssetManagerData beside the app — see Help → Portable mode.

Checksums: SHA256SUMS, NOT signed: no release key was configured.
Every file has a build-provenance attestation:
gh attestation verify <file> --repo gcoxdev/asset-manager