Upgrade default Claude Opus model to 4.8

Bump the default Opus route/model from claude-opus-4-7 to claude-opus-4-8
across provider presets (claude, claudeDesktop, hermes, openclaw, opencode,
universal), i18n locales (zh/en/ja/zh-TW), pricing seed data, and the
user-manual docs.

- Add claude-opus-4-8 pricing row ($5/$25/$0.50/$6.25); keep the 4-7 row
  for historical usage stats (seeded via INSERT OR IGNORE).
- Claude Desktop proxy: accept bidirectional opus 4-7 <-> 4-8 route alias
  during rollout so previously saved routes keep resolving.
- thinking_optimizer: route opus-4-8 through adaptive thinking and normalize
  dotted model ids (also fixes dotted 4-6/4-7 falling back to legacy).
- usage_stats: normalize Bedrock/Vertex/aggregator opus-4-8 ids to base
  pricing.

Also merge role:"system" messages into the Gemini systemInstruction in the
Anthropic->Gemini transform.

src-tauri/src/proxy/providers/copilot_model_map.rs

@@ -324,14 +324,14 @@ mod tests {
 
     #[test]
     fn resolve_falls_back_to_highest_family_version() {
-        // 用户请求 opus 4.7 但 Copilot 账号只有 opus 4.6
+        // 用户请求 opus 4.8 但 Copilot 账号只有 opus 4.6
         let models = vec![
             model("claude-opus-4.5"),
             model("claude-opus-4.6"),
             model("claude-sonnet-4.6"),
         ];
         assert_eq!(
-            resolve_against_models("claude-opus-4.7", &models),
+            resolve_against_models("claude-opus-4.8", &models),
             Some("claude-opus-4.6".to_string())
         );
     }