[FEATURE] Generate SBOMs for container images and filesystems

**Is your feature request related to a problem? Please describe.**
Feature to generate SBOMs for the complete software shipped or deployed in:

- OCI/Docker container images
- Extracted container root filesystems
- Arbitrary filesystem trees, chroots, or installation directories

**Describe the solution you'd like**
Add container-image and filesystem sources to the existing feluda sbom workflow.

Possible CLI design:
```
# Scan a container image
feluda sbom spdx --image nginx:latest --output nginx.spdx.json
feluda sbom cyclonedx --image ghcr.io/example/app@sha256:

# Scan an extracted root filesystem or arbitrary directory
feluda sbom spdx --filesystem ./rootfs --output rootfs.spdx.json
feluda sbom cyclonedx --filesystem /opt/application

# Generate both formats
feluda sbom --image example/app:1.0 --output ./sbom
```

**Describe alternatives you've considered**
syft by anchore is being used currently for this use case.