fix(config): accept spaces and trailing commas in list option values

MEDIA_PROXY_RESOURCE_TYPES and TRUSTED_REVERSE_PROXY_NETWORKS were
validated by splitting the raw value without trimming, while the parser
trims items and skips empty ones. Values such as "image, video" or
"192.168.0.0/16, 10.0.0.0/8", and lists with a trailing comma, failed
startup even though the parser accepts them.

Validate the parsed list instead, and reject values that contain no
items at all so that a comma-only value cannot silently clear the
default media proxy resource types.