Let the menu's click and shift-click actions be swapped

Clicking a profile switched to it exclusively and shift-click opened it
alongside, with no way round for anyone who opens alongside far more often
than they switch. Settings now carries the choice, storing only the plain
click's action — the other gesture gets whatever is left, so the two can't
both end up meaning the same thing, and no migration is needed for anyone
who never touches it.

Switching also quits the other profiles again when the profile clicked is
already up, which e7777d5 had carved out on the reasoning that a click
reaching for a second open window is someone moving between windows rather
than asking for one to go. That guess is what this setting now settles:
with each action bound to a gesture of its own, choosing the switch gesture
is the instruction, and second-guessing it left no way to ask for an
exclusive switch at all once the target was running.

The menu spells out both gestures rather than only the modified one, since
which of them quits things is no longer fixed. Each profile's tooltip
describes what a click will actually do to it as things stand — it promises
to quit the neighbours only when there are neighbours to quit.

README.md

@@ -43,11 +43,15 @@ one is up, dots alone when there are more (hover for the names).
 
 Open the menu and:
 
-- **Click a profile that isn't running** to switch to it. Every other running
-  profile is quit first, so you end up with just that one.
-- **Click a profile that is already running** to bring its window forward,
-  leaving everything else where it is.
-- **Shift-click a profile** to open it *alongside* whatever is already running.
+- **Click a profile** to switch to it. Every other running profile is quit
+  first, so you end up with just that one — including when the profile you
+  clicked is already up, in which case it's the neighbours that go.
+- **Shift-click a profile** to open it *alongside* whatever is already running,
+  or to bring its window forward if it's already up, leaving everything else
+  where it is.
+
+If you open alongside more often than you switch, **Settings → Click a profile
+to** swaps the two around.
 
 A `⇆` marks the profile you last switched to. **Close Profile** quits one
 profile; **Quit Claude** quits all of them and leaves shannoncoat running.
@@ -89,6 +93,8 @@ it's running, it's quit first.
 ## Settings
 
 - **Launch at Login** — start shannoncoat automatically.
+- **Click a profile to** — whether plain click switches and Shift-click opens
+  alongside, or the reverse.
 - **Window tag** — name chip or coloured dot.
 - **Automatically check for updates** — once a day at most.