feat(pricing): add Kimi K3 to built-in model pricing table

Seed kimi-k3 at the official list price ($3/M input, $15/M output,
$0.30/M cache read; released 2026-07-16 with a 1M context window).
Cross-checked against the Moonshot pricing docs, OpenRouter, and
models.dev. Seed-only change: ensure_model_pricing_seeded picks it up
on next launch, no schema version bump needed.

src-tauri/src/database/schema.rs

@@ -2099,6 +2099,7 @@ impl Database {
                 "0.19",
                 "0",
             ),
+            ("kimi-k3", "Kimi K3", "3.00", "15.00", "0.30", "0"),
             // 腾讯混元 (Tencent Hunyuan)（官方 CNY 1/4/0.25 按 1 USD ≈ 7.14 折算；Hy3 阶梯计价取最低档）
             ("hunyuan-hy3", "Hunyuan Hy3", "0.14", "0.56", "0.035", "0"),
             ("hy3", "Hunyuan Hy3", "0.14", "0.56", "0.035", "0"),