feat(whisper): add Distil-Whisper Small and Large v3 as first-class models

Two new registry entries (crates/core/src/model_registry.rs):
- whisper-distil-small-en — 336 MB, ~6× faster than whisper-small-en
- whisper-distil-large-v3 — 1.55 GB, near large-v3 accuracy at medium size

Both are whisper.cpp-compatible GGML binaries hosted on HF by the
distil-whisper org; no runtime change, just wider model choice. English-only
by design (matches upstream Distil-Whisper).

The Settings model picker widens to six options — Tiny, Base, Small,
Distil-S, Medium, Distil-L — ordered roughly by accuracy. Download/load
commands now take the resolved model id (whisper-distil-*) instead of the
lowercased label, so the frontend owns the label↔id mapping.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/core/src/model_registry.rs

@@ -150,6 +150,23 @@ static ALL_MODELS: LazyLock<Vec<ModelEntry>> = LazyLock::new(|| {
             }],
             description: "Accuracy-first English transcription",
         },
+        ModelEntry {
+            id: ModelId::new("whisper-distil-small-en"),
+            engine: Engine::Whisper,
+            display_name: "Distil-Whisper Small (English)",
+            disk_size: Megabytes(336),
+            ram_required: Megabytes(900),
+            speed_tier: SpeedTier::Fast,
+            accuracy_tier: AccuracyTier::Great,
+            languages: LanguageSupport::EnglishOnly,
+            files: vec![ModelFile {
+                filename: "ggml-distil-small.en.bin",
+                url: "https://huggingface.co/distil-whisper/distil-small.en/resolve/main/ggml-distil-small.en.bin",
+                size: Megabytes(336),
+                sha256: None,
+            }],
+            description: "Small accuracy, ~6\u{00d7} faster — distilled variant",
+        },
         ModelEntry {
             id: ModelId::new("whisper-medium-en"),
             engine: Engine::Whisper,
@@ -167,6 +184,23 @@ static ALL_MODELS: LazyLock<Vec<ModelEntry>> = LazyLock::new(|| {
             }],
             description: "Best Whisper accuracy — needs 4+ GB RAM",
         },
+        ModelEntry {
+            id: ModelId::new("whisper-distil-large-v3"),
+            engine: Engine::Whisper,
+            display_name: "Distil-Whisper Large v3 (English)",
+            disk_size: Megabytes(1550),
+            ram_required: Megabytes(2800),
+            speed_tier: SpeedTier::Moderate,
+            accuracy_tier: AccuracyTier::Excellent,
+            languages: LanguageSupport::EnglishOnly,
+            files: vec![ModelFile {
+                filename: "ggml-distil-large-v3.bin",
+                url: "https://huggingface.co/distil-whisper/distil-large-v3-ggml/resolve/main/ggml-distil-large-v3.bin",
+                size: Megabytes(1550),
+                sha256: None,
+            }],
+            description: "Near large-v3 accuracy at ~6\u{00d7} the speed",
+        },
     ]
 });