Refreshes .claude/ skill library: fixes stale refs, adds 4 new skills

- Updates CLAUDE.md tech stack to current versions (Compose 1.10.3, Kotlin 2.3.20).
- Reframes kotlin-multiplatform iOS as mature; adds secp256k1-kmp 0.23.0 references.
- Updates desktop-expert Main.kt references (code grew from ~270 to 1341 lines and
  NavigationRail moved to ui/deck/SinglePaneLayout.kt); replaces obsolete
  "hardcoded ctrl = true" anti-pattern note with accurate isMacOS branching.
- Removes compose-desktop.md (superseded by desktop-expert/).
- Adds nostr-expert references: nip19-bech32, event-factory, crypto-and-encryption,
  large-cache. Adds kotlin-expert/common-utilities, compose-expert/rich-text-parsing,
  android-expert/image-loading.
- New skills: account-state (Account + LocalCache), relay-client (subscriptions,
  filter assemblers, preloaders), feed-patterns (FeedFilter + FeedViewModel family),
  auth-signers (NostrSigner across internal / NIP-46 / NIP-55).

.claude/skills/desktop-expert/references/desktop-navigation.md

@@ -15,7 +15,7 @@ Comparison of mobile vs desktop navigation patterns in AmethystMultiplatform.
 
 ### Current Implementation
 
-**File:** `desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/Main.kt:191-264`
+**File:** `desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/deck/SinglePaneLayout.kt` (NavigationRail begins at L97; `NavigationRailItem`s at L103 and L127+).
 
 ```kotlin
 @Composable
@@ -459,6 +459,6 @@ fun FeedScreen() {
 
 ## References
 
-- **Current Desktop:** Main.kt:191-264
+- **Current Desktop:** `ui/deck/SinglePaneLayout.kt` (NavigationRail L97) and `ui/deck/DeckLayout.kt` (multi-pane)
 - **Material3 NavigationRail:** [Material Design Docs](https://m3.material.io/components/navigation-rail)
 - **Material3 NavigationBar:** [Material Design Docs](https://m3.material.io/components/navigation-bar)