feat: Extract shared UI components to commons for Android/Desktop reuse

Extract reusable components from desktopApp to commons module:

Utilities (commonMain):
- NumberFormatters: countToHumanReadable, countToHumanReadableBytes
- PubKeyFormatter: toShortDisplay, toDisplayHexKey for key formatting

Utilities (jvmAndroid):
- TimeAgoFormatter: Human-readable time formatting for Nostr timestamps
- ZapFormatter: BigDecimal amount formatting with G/M/k suffixes

UI Components (commonMain):
- AppScreen enum for shared navigation
- LoadingState, EmptyState, ErrorState with refresh/retry support
- FeedHeader with relay status indicator
- NoteCard for displaying Nostr notes
- ActionButtons (AddButton, RemoveButton)
- RobohashImage for avatar display
- PlaceholderScreens (Search, Messages, Notifications)
- RelayStatusColors and shared color definitions

UI Components (jvmAndroid):
- LoginCard with key input field
- NewKeyWarningCard for new key backup warnings
- KeyInputField and SelectableKeyText
- ProfileInfoCard for account display
- RelayStatusCard for relay management

Core (jvmAndroid):
- AccountManager with login/logout/key generation
- RelayConnectionManager base class
- RelayStatus and DefaultRelays

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip01Core/core/HexKey.kt

@@ -29,6 +29,9 @@ fun ByteArray.toHexKey(): HexKey = Hex.encode(this)
 
 fun HexKey.hexToByteArray(): ByteArray = Hex.decode(this)
 
+fun HexKey.hexToByteArrayOrNull(): ByteArray? =
+    if (Hex.isHex(this)) Hex.decode(this) else null
+
 const val PUBKEY_LENGTH = 64
 
 const val EVENT_ID_LENGTH = 64