Replace setup CLI stub with iced-based wizard

Lets the user paste an installer URL or local .exe path, downloads to
a temp file if needed, and runs the installer via umu-run with the
launcher's prefix, gameid, and proton path wired up. On completion,
checks for the expected exe and reports next steps.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -26,8 +26,9 @@ Launch / Kill entries. Users can add or remove launchers in `config edit`.
   prefix / exe / ownership / running state.
 - `service` — installs a `systemd --user` unit so the tray autostarts with
   the graphical session.
-- `setup` — prints the manual setup steps for a launcher (a graphical
-  wizard via iced is planned).
+- `setup` — graphical wizard (iced) that downloads an installer URL or
+  accepts a local `.exe`, then runs it via `umu-run` in the launcher's
+  Wine prefix.
 
 ## Install
 
@@ -57,7 +58,7 @@ umutray service install
 | `umutray launch <name>`          | Launch a specific launcher (e.g. `umutray launch epic`) |
 | `umutray kill [<name>]`          | Kill one launcher, or all if no name is given           |
 | `umutray diagnose [<name>]`      | Health checks (one launcher or all)                     |
-| `umutray setup <name>`           | Print setup steps for a launcher                        |
+| `umutray setup <name>`           | Open the graphical setup wizard for a launcher          |
 | `umutray update-proton --latest` | Install newest GE-Proton release                        |
 | `umutray update-proton --list`   | Show recent releases without installing                 |
 | `umutray update-proton`          | Interactive version picker                              |