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- Removes compose-desktop.md (superseded by desktop-expert/).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/nostr-expert/SKILL.md

@@ -514,6 +514,10 @@ Or see `references/nip-catalog.md` for complete catalog.
 - **references/nip-catalog.md** - All 57 NIPs with package locations and key files
 - **references/event-hierarchy.md** - Event class hierarchy, kind classifications, common types
 - **references/tag-patterns.md** - Tag structure, TagArrayBuilder DSL, common tag types, parsing patterns
+- **references/nip19-bech32.md** - `Nip19Parser`, `Bech32Util`, `TlvBuilder`, entity types (NPub, NSec, NEvent, NAddress, NProfile, NRelay, NEmbed)
+- **references/event-factory.md** - `EventFactory` dispatch pattern and how to register a new kind
+- **references/crypto-and-encryption.md** - Event signing/verification, secp256k1 abstraction, NIP-44 encryption, `SharedKeyCache`
+- **references/large-cache.md** - `LargeCache<K,V>` expect/actual + `ICacheOperations` functional API
 - **scripts/nip-lookup.sh** - Find NIP implementations by number or search term
 
 ## Quick Reference