refactor: take nostrPublicKey() from the library, and pin it against NIP-06

The app has carried its own `LocalKeyManager.nostrPublicKey()` in
WalletManagerExtension.kt since before the library's returned anything usable:
the library's gave back `publicKey().toHex()`, the 33-byte compressed encoding,
so the app went through quartz -- `KeyPair(privKey).pubKey.toHexKey()` -- to
get the x-only key that relays, events and npubs actually carry. As of
lightning-kmp-app 84cc44c the library's returns the x-only key too, and the
app's copy is a second implementation of the one value that is every profile's
identity. This deletes it and switches its three callers -- RelaysSocketManager,
NavigationViewModel, CreateProfileViewModel -- to
`fr.acinq.phoenix.managers.nostrPublicKey`.

**The two were proved equal before anything was deleted, not read to be.** They
go through different stacks (quartz's `KeyPair` against bitcoin-kmp's
`xOnly()`), and a difference between them would not fail a build or a test: it
would publish every existing profile under a new key on the next launch, with
nothing on screen to say so. So the first form of the test in this commit built
one `LocalKeyManager` from NIP-06's mnemonic exactly as CreateProfileViewModel
does -- `NodeParamsManager.chain`, `NodeParamsManager.remoteSwapInXpub` -- and
called both functions on it, the library's imported under an alias because the
names collide. Equal on mainnet, which is what the app ships on, and equal on
Testnet3, where the library derives from account 1' instead of 0'. Only then
did the app's go.

**What remains is a pin from the consuming side, anchored to NIP-06 rather than
to a captured output.** A value copied out of a passing run pins the code to
itself; NIP-06 publishes two test vectors -- a twelve-word and a twenty-four-word
mnemonic, empty passphrase, path m/44'/1237'/0'/0/0 -- and that path is the
library's mainnet path exactly, so on the chain the app ships on the answer is
not ours to choose. Both vectors are asserted, and the test also asserts that
`NodeParamsManager.chain` is Mainnet, so a chain change surfaces here as the
moment the published answers stop applying rather than as two mysteriously
failing assertions.

**Quartz stays in the test, as an oracle rather than as an implementation.** The
app signs events with quartz from `nostrPrivateKey()`, and the key it publishes
has to be the one quartz derives for the secret it signs with; that agreement
was the property the deleted copy embodied by construction. It is now stated
once, on mainnet and on Testnet3 -- alongside the shape check, sixty-four
lowercase hex characters, which is the line a revert to the compressed form
(sixty-six) would trip. Off mainnet there is no published vector for account
1', so shape and quartz-agreement are all that is asserted there.

**The test lives in `managers`, not `extensions`.** Its first form sat beside
the function it was checking, in `press.mantra.compose.extensions`. With that
function gone, a test in that package would be about an extension the app no
longer has; `press.mantra.compose.managers` mirrors `fr.acinq.phoenix.managers`,
the library package it pins, and is where the app's other key-material tests
sit. The import in each caller is placed inside the file's sorted
`fr.acinq.phoenix` block rather than where the old `press.mantra` line stood.

:composeApp:compileDebugKotlinAndroid is clean; :composeApp:jvmTest is 736
tests, 0 failures -- the 733 before this change plus the three here.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

composeApp/src/commonMain/kotlin/press/mantra/compose/extensions/WalletManagerExtension.kt

@@ -1,12 +0,0 @@
-package press.mantra.compose.extensions
-
-import com.vitorpamplona.quartz.nip01Core.core.toHexKey
-import com.vitorpamplona.quartz.nip01Core.crypto.KeyPair
-import fr.acinq.lightning.crypto.LocalKeyManager
-import fr.acinq.phoenix.managers.nostrPrivateKey
-
-fun LocalKeyManager.nostrPublicKey(): String {
-    return KeyPair(
-        privKey = nostrPrivateKey().value.toByteArray()
-    ).pubKey.toHexKey()
-}

composeApp/src/commonMain/kotlin/press/mantra/compose/network/relays/RelaysSocketManager.kt

@@ -9,6 +9,7 @@ import com.vitorpamplona.quartz.nip77Negentropy.NegCloseCmd
 import com.vitorpamplona.quartz.nip77Negentropy.NegMsgCmd
 import com.vitorpamplona.quartz.nip77Negentropy.NegOpenCmd
 import fr.acinq.phoenix.data.ActiveWallet
+import fr.acinq.phoenix.managers.nostrPublicKey
 import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
@@ -20,7 +21,6 @@ import kotlinx.coroutines.flow.collectLatest
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
-import press.mantra.compose.extensions.nostrPublicKey
 
 
 /**

composeApp/src/commonMain/kotlin/press/mantra/compose/ui/view/model/CreateProfileViewModel.kt

@@ -17,6 +17,7 @@ import fr.acinq.bitcoin.byteVector
 import fr.acinq.lightning.Lightning
 import fr.acinq.lightning.crypto.LocalKeyManager
 import fr.acinq.phoenix.managers.NodeParamsManager
+import fr.acinq.phoenix.managers.nostrPublicKey
 import fr.acinq.phoenix.managers.nsecPassword
 import fr.acinq.phoenix.utils.MnemonicLanguage
 import kotlinx.coroutines.CoroutineExceptionHandler
@@ -24,7 +25,6 @@ import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.IO
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
-import press.mantra.compose.extensions.nostrPublicKey
 import kotlin.time.Duration.Companion.seconds
 
 class CreateProfileViewModel(

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

@@ -9,6 +9,7 @@ import press.mantra.compose.ui.composable.navigation.routes.SovereignWalletStart
 import press.mantra.compose.ui.view.state.NavigationUIState
 import co.touchlab.kermit.Logger
 import fr.acinq.phoenix.data.ActiveWallet
+import fr.acinq.phoenix.managers.nostrPublicKey
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.IO
@@ -21,7 +22,6 @@ import kotlinx.coroutines.flow.distinctUntilChanged
 import kotlinx.coroutines.flow.firstOrNull
 import kotlinx.coroutines.flow.getAndUpdate
 import kotlinx.coroutines.launch
-import press.mantra.compose.extensions.nostrPublicKey
 import kotlin.time.Duration.Companion.milliseconds
 
 class NavigationViewModel(