feat(pricing): add Claude Sonnet 5 model pricing

Seed claude-sonnet-5 at Anthropic list price ($3/$15 in/out, $0.30/$3.75 cache read/write per Mtok, matching Sonnet 4.6). The introductory $2/$10 promo through 2026-08-31 is intentionally not seeded. Applied on next app start via ensure_model_pricing_seeded; no SCHEMA_VERSION bump.

src-tauri/src/database/schema.rs

@@ -1301,6 +1301,15 @@ impl Database {
                 "0.50",
                 "6.25",
             ),
+            // Claude Sonnet 5（list 价，与 Sonnet 4.6 一致；促销 $2/$10 至 2026-08-31 不入表）
+            (
+                "claude-sonnet-5",
+                "Claude Sonnet 5",
+                "3",
+                "15",
+                "0.30",
+                "3.75",
+            ),
             // Claude 4.7 系列
             (
                 "claude-opus-4-7",