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.

Cargo.lock

@@ -838,15 +838,19 @@ name = "erp-config"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "async-trait",
  "axum",
  "chrono",
  "erp-core",
  "sea-orm",
  "serde",
  "serde_json",
+ "thiserror",
  "tokio",
  "tracing",
+ "utoipa",
  "uuid",
+ "validator",
 ]
 
 [[package]]
@@ -891,6 +895,7 @@ dependencies = [
  "config",
  "erp-auth",
  "erp-common",
+ "erp-config",
  "erp-core",
  "erp-server-migration",
  "redis",