feat(identity): a switch that tears down what it should

Phase 2 of docs/multiple-profiles.md. The transition, made correct, with
nothing yet calling it from a screen: the view model, one manager, and three
one-line actuals.

switchToWallet becomes switchToIdentity, and does what a switch is: remember
which one, set startWalletImmediately back to true -- a switch is the user
saying which one, and the flag was only ever the user saying "show me the
list"; nothing set it back before because nothing could switch -- clear the
active identity, and stop the node of the profile being left, if it had one.
The identity is cleared before the node is stopped, so that every collector
that could reach the business is cancelled before the stop runs. The test is
business != null, not the kind: whether the profile being left has a node
behind it is the fact, and the kind is how it currently comes to be true.
stopPlatformBusiness is an expect beside updateBusinessActiveInUI, for the
reason that one is: BusinessManager is a per-platform object. Its three
actuals call stopBusiness, which existed on every platform and nothing
called. The manager is injected into the view model as a function so that
the branch can be pinned without a node.

RelaysSocketManager.observeActiveUserId becomes a child of collectLatest --
the shape the pumps and the notary already had. It used to keep one job per
pubkey on its own scope and cancel only the job for the pubkey being
started, which meant a switch left the previous identity's observer running:
two observers feeding updateRelayPools, and the one pool following whichever
relay list emitted last. The map goes; a null identity closes nothing, since
the pool is shared by pumps a null identity has already cancelled, and the
next identity's list replaces it through changeRelays as it always did. The
scope is injectable and relayUrls is exposed, both for the test.

The sign-in and create tails keep their own navigate beside the observer's,
now with a comment saying why: the navigation state is a StateFlow, an
update to a state equal to the current one emits nothing, and the explicit
navigation is what guarantees the stack moves even on the day the state
does not.

Tests: IdentitySwitchJvmTest, through the real SovereignWalletViewModel with
a real notary and navigation machine on an in-memory database -- A open and
a kind 1 queued for A is signed; switch to B, the identity clears, the
machine goes to startup, B is activated the way startup does and routed from
its account; a kind 1 queued for A now waits three seconds unsigned, and
goes out when A is back. Leaving a profile with a PhoenixBusiness behind it
-- constructible without a node, since everything in it is lazy -- stops
that node once; leaving nothing, or a bare key, stops nothing.
RelaysSocketManagerSwitchJvmTest over a fake relay repository and fake
sockets: after the switch the pool holds B's relays, a re-emission of A's
list changes nothing -- the line that fails against the old observer -- and
an identity whose list is still empty leaves the pool as it was, which is
the behaviour updateRelayPools has always had for an empty list.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Pulled-From: curated/curated@9b3a19278f

composeApp/src/iosMain/kotlin/press/mantra/compose/ui/view/model/NavigationViewModel.ios.kt

@@ -15,6 +15,10 @@ actual fun updateBusinessActiveInUI(walletId: WalletId) {
     BusinessManager.updateBusinessActiveInUI(walletId)
 }
 
+actual fun stopPlatformBusiness(walletId: WalletId) {
+    BusinessManager.stopBusiness(walletId)
+}
+
 actual fun loadAndDecryptSeed(phoenixGlobal: PhoenixGlobal): DecryptSeedResult {
     return SeedManager.loadAndDecrypt(
         phoenixGlobal