feat(config): add system configuration module (Phase 3)

Implement the complete erp-config crate with:
- Data dictionaries (CRUD + items management)
- Dynamic menus (tree structure with role filtering)
- System settings (hierarchical: platform > tenant > org > user)
- Numbering rules (concurrency-safe via PostgreSQL advisory_lock)
- Theme and language configuration (via settings store)
- 6 database migrations (dictionaries, menus, settings, numbering_rules)
- Frontend Settings page with 5 tabs (dictionary, menu, numbering, settings, theme)

Refactor: move RBAC functions (require_permission) from erp-auth to erp-core
to avoid cross-module dependencies.

Add 20 new seed permissions for config module operations.

crates/erp-config/src/lib.rs

@@ -1 +1,10 @@
-// erp-config: 系统配置模块 (Phase 3)
+pub mod config_state;
+pub mod dto;
+pub mod entity;
+pub mod error;
+pub mod handler;
+pub mod module;
+pub mod service;
+
+pub use config_state::ConfigState;
+pub use module::ConfigModule;