fix: resolve remaining Kotlin compiler warnings in commons and cli

- Suppress DEPRECATION on REASONABLE_SIGN_KINDS, which intentionally lists the
  deprecated TorrentCommentEvent kind.
- Replace deprecated readLine() with readlnOrNull() in SecureKeyStorage.
- Drop unnecessary !! non-null assertions in KeyCommands and NostrConnect where
  the receiver is already smart-cast to non-null.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018nqdy4VTLKidUWzGTJPja9

cli/src/main/kotlin/com/vitorpamplona/amethyst/cli/commands/KeyCommands.kt

@@ -77,7 +77,7 @@ object KeyCommands {
             Output.emit(mapOf("valid" to false))
             return 0
         }
-        val npub = hex!!.hexToByteArray().toNpub()
+        val npub = hex.hexToByteArray().toNpub()
         Output.emit(mapOf("valid" to true, "pubkey" to hex, "npub" to npub))
         return 0
     }

cli/src/main/kotlin/com/vitorpamplona/amethyst/cli/commands/NostrConnect.kt

@@ -81,7 +81,7 @@ object NostrConnect {
             }
         }
         if (secret == null) return null
-        return Offer(clientPubkey, relays, secret!!, name)
+        return Offer(clientPubkey, relays, secret, name)
     }
 
     private fun buildOffer(