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>

src/lib/types/app.ts

@@ -3,7 +3,13 @@ export type FontFamily = "lexend" | "atkinson" | "opendyslexic";
 export type ReduceMotion = "system" | "on" | "off";
 export type RecordingEngine = "whisper" | "parakeet";
 export type FormatMode = "Raw" | "Clean" | "Smart";
-export type WhisperModelSize = "Tiny" | "Base" | "Small" | "Medium";
+export type WhisperModelSize =
+  | "Tiny"
+  | "Base"
+  | "Small"
+  | "Distil-S"
+  | "Medium"
+  | "Distil-L";
 export type AiTier = "off" | "cleanup" | "tasks";
 export type LlmModelIdStr = "qwen3_1_7b" | "qwen3_4b_instruct_2507" | "qwen3_14b";
 export type TaskBucket = "inbox" | "today" | "soon" | "later";