feat: Add Compose Multiplatform Desktop support foundation

- Add desktopApp module with JVM entry point and sidebar navigation
- Add Claude specs for AI-assisted development:
  - Agent definitions: nostr-protocol, kotlin-multiplatform, compose-ui, kotlin-coroutines
  - Skills: quartz-kmp conversion, compose-desktop patterns
  - Commands: desktop-run, nip, extract
- Update Gradle configuration with Compose Multiplatform 1.7.1 plugin
- Add coroutines and secp256k1 JVM dependencies to version catalog

Next steps:
- Convert Quartz library to full KMP (expect/actual for crypto)
- Implement relay connections in desktop app
- Share UI components between Android and Desktop

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

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

.claude/commands/desktop-run.md

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+---
+description: Build and run the desktop app
+---
+
+Build and run the Amethyst Desktop application:
+
+```bash
+./gradlew :desktopApp:run
+```
+
+## Troubleshooting
+
+If the build fails, check:
+
+1. **JDK Version**: Requires JDK 17+
+   ```bash
+   java -version
+   ```
+
+2. **Compose Multiplatform Plugin**: Verify version in `gradle/libs.versions.toml`
+
+3. **Quartz Build**: Ensure Quartz compiles first
+   ```bash
+   ./gradlew :quartz:build
+   ```
+
+4. **Desktop Dependencies**: Check `desktopApp/build.gradle.kts` has:
+   ```kotlin
+   implementation(compose.desktop.currentOs)
+   ```
+
+## Creating Distributable
+
+```bash
+# macOS
+./gradlew :desktopApp:packageDmg
+
+# Windows
+./gradlew :desktopApp:packageMsi
+
+# Linux
+./gradlew :desktopApp:packageDeb
+```
+
+Outputs will be in `desktopApp/build/compose/binaries/`

.claude/commands/extract.md

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+---
+description: Extract a composable from amethyst to shared code
+---
+
+Extract the component `$ARGUMENTS` from the Android app to shared KMP code:
+
+## Process
+
+1. **Locate the component** in the amethyst module:
+   ```bash
+   find amethyst/src -name "*$ARGUMENTS*" -o -name "*$ARGUMENTS*"
+   grep -r "fun $ARGUMENTS\|class $ARGUMENTS" amethyst/src/
+   ```
+
+2. **Analyze dependencies**:
+   - Android-specific imports (Context, Intent, etc.)
+   - Platform APIs (Camera, MediaStore, etc.)
+   - Android Compose specifics vs standard Compose
+
+3. **Identify what can be shared**:
+   - Pure Composable functions → `shared-ui/commonMain/`
+   - Business logic → `quartz/commonMain/`
+   - Platform-specific → create expect/actual
+
+4. **Create shared version**:
+   - Move to appropriate shared module
+   - Replace Android imports with multiplatform alternatives
+   - Add expect declarations for platform-specific parts
+
+5. **Update references**:
+   - Change imports in amethyst module
+   - Add implementations in desktopApp if needed
+
+## Common Replacements
+
+| Android | Multiplatform |
+|---------|---------------|
+| `LocalContext.current` | expect/actual or parameter |
+| `stringResource()` | `Res.string.*` |
+| `painterResource()` | `painterResource(Res.drawable.*)` |
+| `Toast.makeText()` | Custom snackbar/notification |
+| `Intent` | expect/actual for navigation |
+
+## Example
+
+```
+/extract NoteCard
+```
+
+This will find NoteCard, analyze its dependencies, and guide you through extracting it to shared code.

.claude/commands/nip.md

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+---
+description: Get NIP specification and implementation guidance
+---
+
+Fetch and explain NIP-$ARGUMENTS from the Nostr protocol:
+
+1. **Get the specification** from https://github.com/nostr-protocol/nips/blob/master/$ARGUMENTS.md
+
+2. **Show key details**:
+   - Event kind(s) used
+   - Required and optional fields
+   - Tag structure
+   - Message flow between client and relay
+
+3. **Check implementation status** in Quartz:
+   ```bash
+   grep -r "NIP-$ARGUMENTS\|nip$ARGUMENTS\|kind.*=" quartz/src/
+   ```
+
+4. **Provide implementation guidance**:
+   - Which Quartz classes to use or create
+   - Event construction example
+   - Relay subscription filters
+   - Verification/validation logic
+
+## Example Usage
+
+```
+/nip 01    # Basic protocol
+/nip 44    # Versioned encryption
+/nip 57    # Zaps
+```