Fix bugs: humanizeBytes panic, IP range logic, dead code, and error handling

[jadolg]

• server.go: Fix potential index out of bounds panic in humanizeBytes
• validation.go: Fix lexicographic string comparison in parseIPRange that incorrectly classified 172.2.x.x and 172.3.x.x as private addresses; remove duplicate dead-code block in validateRegistry that was unreachable
• image.go: Propagate json.Marshal errors in createLayerMetadata, createDockerManifest, and createRepositoriesFile instead of silently writing empty/corrupted data to disk
• registry.go: Cap error response body reads at 4 KB with io.LimitReader to prevent unbounded memory consumption from a misbehaving registry