add a transmission sidecar and ui

officer-transmission is a new pm2 peer that owns the transmission rpc
connection and exposes a curated /_officer/* contract instead of proxying
raw rpc. it absorbs the three quirks callers otherwise have to know about:
the 409 x-transmission-session-id handshake, failures returned as
{"result": "..."} inside http 200, and basic auth where an empty username
must send no header at all.

/transmission is the ui, on the workspace/panel framework: a filter nav and
three sections (torrents, stats, settings). the torrent list is virtualised
with 30 available columns, multi-select, and a right-click menu; the detail
pane covers general, files as a real tree, peers and trackers. filters and
the open torrent live in the url, so a filtered view is a link.

phase 1 goal was parity with _references/transmission-web. follow-up work is
recorded in TODO.md.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/sidecar/protocol.ts

@@ -70,6 +70,8 @@ export type SidecarEvent =
   | { type: 'slskd:server'; port: number }
   // Headscale — the sidecar reports where its HTTP server is listening (random port) on connect
   | { type: 'headscale:server'; port: number }
+  // Transmission — the sidecar reports where its HTTP server is listening (random port) on connect
+  | { type: 'transmission:server'; port: number }
   // Generic
   | { type: 'error'; id?: string; error: string };