feat: Add relay connections, login, and feed view to desktop app

- Add DesktopHttpClient and DesktopRelayConnectionManager for relay WebSocket connections
- Implement AccountManager with key generation and nsec/npub login support
- Create LoginScreen with key import and new key generation UI
- Build FeedScreen with live global feed subscription and note cards
- Add ProfileScreen showing account info and logout
- Update RelaySettingsScreen with connection status and relay management
- Configure JDK 21 toolchain for desktop builds
- Add shared UI analysis documentation

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

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

desktopApp/build.gradle.kts

@@ -6,6 +6,17 @@ plugins {
     alias(libs.plugins.jetbrainsComposeCompiler)
 }
 
+sourceSets {
+    main {
+        kotlin.srcDir("src/jvmMain/kotlin")
+        resources.srcDir("src/jvmMain/resources")
+    }
+}
+
+kotlin {
+    jvmToolchain(21)
+}
+
 dependencies {
     implementation(compose.desktop.currentOs)
     implementation(compose.material3)