fix: clear compiler warnings across all modules

Sweep of Kotlin compiler warnings in every module's main source sets
(quartz, commons, cli, desktopApp, amethyst, nappletHost).

Genuine code fixes:
- Drop unnecessary !!/safe-calls and redundant elvis/casts (OkHttp's
  now-non-null `body`, smart-cast callbacks, non-null String receivers).
- Remove provably-redundant conditions (`canvas == null` after a
  non-null content check; `account != null` implied by `canModerate`).
- Migrate deprecated kotlinx.collections.immutable persistent ops
  (add/remove/put/addAll -> adding/removing/putting/addingAll).
- Migrate LocalClipboardManager -> LocalClipboard (+ scoped setText),
  ContextCompat.startActivity -> context.startActivity, TabRow ->
  SecondaryTabRow, and @ConsistentCopyVisibility on a private-ctor data class.
- Delete dead ReceiveDialog.onGenerate param (never invoked).
- Fix a platform-Boolean type-mismatch on a ThreadLocal read.

Deprecations with no available successor are narrowly @Suppress-ed with
a reason: androidx.security.crypto (EncryptedSharedPreferences/MasterKey),
androidx.privacysandbox.ui, WebView.databaseEnabled, BluetoothDevice
.connectGatt, media3 setEnableAudioTrackPlaybackParams, FirebaseMessaging
.token, and InputMethodManager.SHOW_IMPLICIT.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015Xb9YbBqhdZsHxMzitmyvn

cli/src/main/kotlin/com/vitorpamplona/amethyst/cli/Context.kt

@@ -300,7 +300,7 @@ class Context(
                         .header("Accept", "application/nostr+json")
                         .build()
                 okhttp.newCall(request).execute().use { resp ->
-                    resp.body?.string()?.let { Nip11RelayInformation.fromJson(it) }
+                    resp.body.string().let { Nip11RelayInformation.fromJson(it) }
                 }
             }.getOrNull()
         }

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

@@ -380,7 +380,7 @@ object BuzzCommands {
                         .get()
                         .build(),
                 ).execute()
-                .use { it.code to (it.body?.string() ?: "") }
+                .use { it.code to it.body.string() }
         }
 
     private suspend fun httpPost(
@@ -392,7 +392,7 @@ object BuzzCommands {
         withContext(Dispatchers.IO) {
             val builder = Request.Builder().url(url).post(body.toRequestBody(jsonMedia))
             if (auth != null) builder.header("Authorization", auth)
-            http.newCall(builder.build()).execute().use { it.code to (it.body?.string() ?: "") }
+            http.newCall(builder.build()).execute().use { it.code to it.body.string() }
         }
 
     /** `buzz post RELAY GID <text>` → publishes a kind-40002 stream message with an `h` tag. */
@@ -578,7 +578,7 @@ object BuzzCommands {
                     .groupBy { it.slug() }
                     .values
                     .mapNotNull { versions -> versions.maxByOrNull { it.createdAt } }
-                    .sortedBy { it.personaOrNull()?.displayName ?: it.slug() ?: "" }
+                    .sortedBy { it.personaOrNull()?.displayName ?: it.slug() }
                     .map {
                         val content = it.personaOrNull()
                         mapOf(

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

@@ -113,7 +113,7 @@ object GitPatchCommands {
                     "event_id" to signed.id,
                     "kind" to signed.kind,
                     "repository" to Address.assemble(addr.kind, addr.pubKeyHex, addr.dTag),
-                    "subject" to (signed as? GitPatchEvent)?.subject(),
+                    "subject" to signed.subject(),
                 ) + RawEventSupport.ackFields(ack),
             )
             return 0

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

@@ -133,6 +133,7 @@ object GitReadCommands {
      * comment trees and PR-update (1619) events (which use NIP-22 uppercase `E`)
      * are out of scope here.
      */
+    @Suppress("DEPRECATION") // legacy kind:1622 GitReplyEvent is read for backward compatibility.
     suspend fun thread(
         dataDir: DataDir,
         rest: Array<String>,