Update Jellyfin plugin release workflow to use MD5 checksums instead of SHA256. Modify manifest.json with new source URL and checksum, and update README to clarify checksum verification process.

.gitea/workflows/release_jellyfin_plugin.yml

@@ -140,7 +140,7 @@ jobs:
               exit 1
             fi
             ARTIFACT_NAME=$(basename "$ARTIFACT")
-            CHECKSUM=$(sha256sum "$ARTIFACT" | awk '{print $1}')
+            CHECKSUM=$(md5sum "$ARTIFACT" | awk '{print $1}')
 
             BODY=$(printf 'Jellyfin plugin **%s** %s\n\nBuilt automatically from Jellyfin/%s changes.' "$SLUG" "$VERSION" "$SLUG")
             BODY_JSON=$(printf '%s' "$BODY" | jq -Rs .)