feat: add project profiles for snapshot-based config switching

Add a profile feature that captures the current provider, MCP,
skills and prompt state for Claude Code and Codex as a named
snapshot, and re-applies it in one click from the header switcher
or the tray Projects submenu.

- New profiles table (schema v12) with current marker in settings
- ProfileService orchestrates the four existing switch primitives
  (provider first, then MCP diff, skills diff, prompt enable)
- Best-effort apply: dangling references become warnings, no rollback
- Header combobox switcher + snapshot-style manage dialog
- Tray Projects submenu shared with the UI apply/event pipeline
- i18n for zh/en/ja/zh-TW under the new profiles domain
- Integration tests covering roundtrip, dangling refs and clear

src-tauri/src/database/dao/mod.rs

@@ -4,6 +4,7 @@
 
 pub mod failover;
 pub mod mcp;
+pub mod profiles;
 pub mod prompts;
 pub mod providers;
 pub mod providers_seed;
@@ -15,5 +16,6 @@ pub mod universal_providers;
 pub mod usage_rollup;
 
 // 所有 DAO 方法都通过 Database impl 提供，无需单独导出
-// 导出 FailoverQueueItem 供外部使用
+// 导出 FailoverQueueItem / Profile 供外部使用
 pub use failover::FailoverQueueItem;
+pub use profiles::Profile;