Add account-level multi-line configuration for emby_remote mounts.
Lines are stored in strm_accounts.config as a urls JSON array with
backward compatibility for the legacy single url field. The backend
automatically fails over to the next line on connection errors and
persists the working active_line index.
Frontend: multi-line editor on Emby mount page and STRM account dialog
with add/remove/reorder, line names, and URL validation.
Co-authored-by: Cursor Agent <cursoragent@cursor.com>
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