webui: replace nautctl web server with a loadable plugin

Drop the web UI that was compiled into nautctl and serve the
torrent-ui front end (../torrent-ui/public) from a native plugin
(plugins/webui) loaded via `nautd --plugin`. The plugin talks to the
engine only through the host call_rpc ABI and adapts the daemon's RPC
surface to the qBittorrent-style contract the UI expects (snapshot/SSE,
torrent detail tabs, add/delete, cookie auth).

Also folds in the daemon refactor that owns per-torrent worker threads
and the swarm engine (naut_swarm) used by the plugin's data source.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/anime_sort.lua

@@ -10,9 +10,9 @@
 -- without waiting for the rest of the torrent.
 --
 -- Install:
---   nautd --socket /tmp/nautd.sock --script examples/anime_sort.lua
---   nautctl --socket /tmp/nautd.sock add_torrent \
---     '{"torrent_id":1,"torrent":"show.torrent","root":"/downloads/1"}'
+--   nautd --socket /tmp/nautd.sock
+--   nautctl --socket /tmp/nautd.sock script examples/anime_sort.lua
+--   nautctl --socket /tmp/nautd.sock add show.torrent /downloads/1
 --
 -- The parser below is a VERBATIM COPY of examples/anitomy.lua (the sandbox has
 -- no `require`, so it must be inlined). Keep the two in sync; examples/
@@ -22,7 +22,7 @@
 -- CONFIG — edit these
 ----------------------------------------------------------------------
 
-local SORTED_ROOT       = "/sorted"   -- destination library root
+local SORTED_ROOT       = "/workspaces/source/ai-garbo/Naut-Torrent/sorted"   -- destination library root
 local ONLY_VIDEO        = true        -- skip non-video files (subs, nfo, samples)
 local KEEP_ORIGINAL_NAME = false      -- true: keep the original filename;
                                       -- false: rename to "Title - SNNENN.ext"