feat(daemon): make the download folder a live setting in both modes

The full-surface audit found the settings story half-true: `config set
download_dir` and the TUI's settings form edited a file a running daemon
never rereads, while the attached TUI displayed the laptop's path and
discarded the edit entirely.

- `download.set_dir`: a session-wide move, published in the contract;
  the per-transfer destination stays refused. `daemon.status` reports
  it and the next transfer lands there.
- `config set download_dir` and `config set shared_dirs` push to a
  live daemon the way `shares add` does, through one shared helper;
  the socket probe is paid only by the keys a daemon owns.
- The attached TUI seeds its settings form from the daemon's status,
  pushes both folders over the socket as typed, reports a partial
  refusal as exactly that, and creates no client-side directories. It
  reads the daemon token from the resolved config — with the token only
  in config.toml it could not attach over TCP — and settings
  persistence honours --config instead of hard-coding the default path.
- `search.wishlist` records a start time, so an attached window
  renders it as running rather than instantly finished.

The rest is the coverage the audit demanded: CLI-level token auth
(wrong, missing, and valid over TCP), `daemon status|stop` with
nothing running, --sort, --limit, --pick first, --password-cmd,
--log-file, --upload-slots, the config-named download folder in both
modes, and headless settings-form tests attached and local. Every
guard was checked by disabling what it protects. Both e2e modes run
green: 94 CLI tests each way, 16 protocol, 285 unit, 34 lib.

soulseek-rs/src/SKILL.md

@@ -58,8 +58,9 @@ So: **one daemon, then as many commands as you like.** Reach for `--no-daemon`
 only when you deliberately want an isolated session, and expect to justify it.
 
 Two things change while a daemon is running: files land in the *daemon's*
-download directory (`daemon status` reports which), and `shares add` updates it
-straight away rather than at its next start.
+download directory (`daemon status` reports which), and `shares add` or
+`config set download_dir` update it straight away rather than at its next
+start.
 
 ## The contract