feat(providers): seed an official preset on startup for Claude/Codex/Gemini

New and existing users now see a built-in "Claude Official" / "OpenAI
Official" / "Google Official" entry in their provider list, so switching
back to the official endpoint is one click away instead of buried in the
README.

- New providers_seed.rs holds the three seeds (id, name, settings_config,
  icon) keyed by AppType, with a single is_official_seed_id() helper that
  scans OFFICIAL_SEEDS so the id list has one source of truth.
- Database::init_default_official_providers() runs once per database
  (gated by an official_providers_seeded setting flag), appends each seed
  to the end of the sort order, and never touches is_current.
- Startup also auto-imports the live config (settings.json / auth.json /
  .env) as a "default" provider before seeding, so users with an existing
  manual config don't lose it when they click the official preset.
- Database::has_non_official_seed_provider() replaces the get_all_providers
  call in import_default_config's gating check with an id-only scan,
  dropping the N+1 endpoint sub-queries from every startup.

src-tauri/src/lib.rs

@@ -467,6 +467,41 @@ pub fn run() {
                 Err(e) => log::warn!("✗ Failed to read skills migration flag: {e}"),
             }
 
+            // 1.5. 自动导入 live 配置 + seed 官方预设供应商（Claude / Codex / Gemini）
+            //
+            // 先 import 后 seed 是有意为之：先把用户手动配置的 settings.json / auth.json / .env
+            // 落成 "default" provider 设为 current，再追加官方预设（is_current=false）。
+            // 这样用户切到官方预设时，回填机制会保护原 live 配置不丢失。
+            for app_type in
+                crate::app_config::AppType::all().filter(|t| !t.is_additive_mode())
+            {
+                match crate::services::provider::import_default_config(
+                    &app_state,
+                    app_type.clone(),
+                ) {
+                    Ok(true) => log::info!(
+                        "✓ Imported live config for {} as default provider",
+                        app_type.as_str()
+                    ),
+                    Ok(false) => log::debug!(
+                        "○ {} already has providers; live import skipped",
+                        app_type.as_str()
+                    ),
+                    Err(e) => log::debug!(
+                        "○ No live config to import for {}: {e}",
+                        app_type.as_str()
+                    ),
+                }
+            }
+
+            match app_state.db.init_default_official_providers() {
+                Ok(count) if count > 0 => {
+                    log::info!("✓ Seeded {count} official provider(s)");
+                }
+                Ok(_) => {}
+                Err(e) => log::warn!("✗ Failed to seed official providers: {e}"),
+            }
+
             // 2. OMO 配置导入（当数据库中无 OMO provider 时，从本地文件导入）
             {
                 let has_omo = app_state