feat(daemon): route commands and the TUI through a running daemon

Session::open attaches to a daemon when one is reachable and logs in
otherwise, so every existing command works unchanged against either. A local
socket is found automatically, which is what makes an agent's invocation need
no flags at all; --no-daemon opts out.

Commands now read identity, shares, server, and download directory from the
session rather than from this run's config: routed to a daemon those differ,
and the session is the one actually on the network. Without that, whoami
named the wrong server and shares reindex would have imposed the client
machine's folders on the daemon.

soulseek-rs/src/SKILL.md

@@ -106,6 +106,18 @@ the interval the server sets and prints `search`-shaped objects for what it
 finds, so one long-running process covers both halves of being a good
 participant.
 
+**`daemon`** — stay logged in as a service other commands share. Prints
+progress on stderr and nothing on stdout; it does not return until stopped.
+While it runs, every other command on this machine uses its session
+automatically — no flags, no credentials, no second login. `--bind ADDR` also
+accepts connections from other machines, which need the token.
+**`daemon status`** — one object: `user`, `server`, `version`, `protocol`,
+`listening`, `listen_port`, `shared_folders`, `shared_files`, `download_dir`,
+`session_loss`, `clients`, `uptime_secs`. Exit 3 when nothing is running.
+**`daemon stop`** — ask it to shut down; prints nothing.
+**`daemon token`** — the secret a client on another machine needs. Local
+clients never need it.
+
 **`shares list`** — one object per configured folder: `directory`, `usable`.
 **`shares add <directory>`** and **`shares remove <directory>`** — change the
 config file; they print nothing.
@@ -152,8 +164,27 @@ is the normal way to be selective.
 ## Running several at once
 
 The server allows one session per account, and the later login wins: two runs
-sharing a username silently kill each other's session. Give every concurrent
-run its own name.
+sharing a username silently kill each other's session.
+
+The daemon is the answer to this. Start one, and every command afterwards
+borrows its session instead of opening one:
+
+```bash
+soulseek-rs daemon &          # once
+soulseek-rs search 'gary beck fold' --json   # no login, no flags
+soulseek-rs search 'marcal steady' --json    # concurrent, same session
+```
+
+Commands find it on their own: it listens on a Unix socket only you can open,
+so there is nothing to configure and no token to pass. `daemon status` says
+whether one is running. This also makes downloads outlive the command that
+started them — the transfer belongs to the daemon, so the queue survives.
+
+Two things change when a daemon is in play: files land in the *daemon's*
+download directory, and `--no-daemon` is how one run opts out and logs in for
+itself.
+
+Without a daemon, give every concurrent run its own name instead:
 
 ```bash
 for q in 'gary beck fold' 'marcal steady'; do