Accept --root after the subcommand

`money serve --root DIR` failed because --root was only read before the
subcommand; after it, the flag reached serve's own flag set, which knows
only --addr, and was rejected. It is too natural a thing to type to refuse,
so run now lifts --root/--root=DIR out of any subcommand's arguments before
they are parsed. A bare `--` still ends it, and given on both sides, the one
after the command wins.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -30,7 +30,7 @@ build changes its shape, delete it and run `money import` again.
 
 Checked in order, first one wins:
 
-1. `--root DIR` on the command line
+1. `--root DIR` on the command line, before or after the command
 2. `$MONEY_ROOT`
 3. the `root` key in `$XDG_CONFIG_HOME/money/config.toml`, which is
    `~/.config/money/config.toml` unless `XDG_CONFIG_HOME` says otherwise