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/config_state.rs

@@ -0,0 +1,11 @@
+use erp_core::events::EventBus;
+use sea_orm::DatabaseConnection;
+
+/// Config-specific state extracted from the server's AppState via `FromRef`.
+///
+/// Contains the database connection and event bus needed by config handlers.
+#[derive(Clone)]
+pub struct ConfigState {
+    pub db: DatabaseConnection,
+    pub event_bus: EventBus,
+}