Embed rspamd-symbols.json in the binary to provide human-readable
descriptions for rspamd symbols in reports. Optionally fetch fresh
symbols from a configurable rspamd API URL (--rspamd-api-url flag),
falling back to the embedded list on error. Update the frontend to
display descriptions alongside symbol names and scores.
Add params field to SpamTestDetail, update RspamdResult.symbols to
reference SpamTestDetail instead of the now-removed RspamdSymbol schema,
and update Go code accordingly.
