Transcription: dwindle model choice to Whisper Base + Whisper Large v3

Registry now lists exactly two models instead of five:
- 'Whisper Base' — names the actual bundled model (was 'Base (default)').
- 'Whisper Large v3' — kept; honest copy on size/speed/RAM.
tiny/small/medium removed from the registry (validate_model_name now
rejects them; existing rows keep their saved model — all current data
is 'base', still valid).
Detail screen shows the model that WILL run by real display name
('Whisper Base (default)') instead of 'Use default (base)'; the picker
lists the two models with the default marked inline.
Backend 78 passed/1 skipped; app 34/34; engine hot-reloaded clean.

app/src/main/kotlin/com/shonar/desktop/Screens.kt

@@ -601,24 +601,24 @@ fun DetailScreen(state: DesktopState) {
                 }
             }
         }
-        // Model override: "Use default" or a specific size.
+        // Model override: shows the model that WILL run, by its real name.
         Row(verticalAlignment = Alignment.CenterVertically) {
             Text("Model: ", style = MaterialTheme.typography.bodyMedium)
-            val current = detail.overrideModel
-                ?: models?.defaultModel
-                ?: "base"
+            val current = detail.overrideModel ?: models?.defaultModel ?: "base"
+            val currentLabel = models?.byName(current)?.displayName ?: current
             TextButton({ showModels = !showModels }) {
-                Text(if (detail.overrideModel == null) "Use default ($current)" else current)
+                Text(if (detail.overrideModel == null)
+                    "$currentLabel (default)" else currentLabel)
             }
         }
         if (showModels && models != null) {
             Column(verticalArrangement = Arrangement.spacedBy(4.dp)) {
-                ModelRow(state, detail, null, models.defaultModel,
-                    "Use default (${models.defaultModel})", "")
                 models.models.forEach { m ->
                     ModelRow(state, detail, m.name, models.defaultModel,
-                        m.displayName, m.description +
-                            (if (!m.available) " — not downloaded" else ""))
+                        m.displayName + (if (m.name == models.defaultModel)
+                            " (default)" else ""),
+                        m.description +
+                            (if (!m.available) " — downloads ~once from the app" else ""))
                 }
             }
             Spacer(Modifier.height(4.dp))