refactor: split architecture rules into domain-specific files

Split the monolithic .architecture-rules.yaml (1700+ lines) into focused
domain-specific files in .architecture-rules/ directory:

- _main.yaml: Core config, principles, ignore patterns, severity levels
- api.yaml: API endpoint rules (API-001 to API-005)
- service.yaml: Service layer rules (SVC-001 to SVC-007)
- model.yaml: Model rules (MDL-001 to MDL-004)
- exception.yaml: Exception handling rules (EXC-001 to EXC-005)
- naming.yaml: Naming convention rules (NAM-001 to NAM-005)
- auth.yaml: Auth and multi-tenancy rules (AUTH-*, MT-*)
- middleware.yaml: Middleware rules (MDW-001 to MDW-002)
- frontend.yaml: Frontend rules (JS-*, TPL-*, FE-*, CSS-*)
- language.yaml: Language/i18n rules (LANG-001 to LANG-010)
- quality.yaml: Code quality rules (QUAL-001 to QUAL-003)

Also creates scripts/validators/ module with base classes for future
modular validator extraction.

The validate_architecture.py loader now auto-detects and merges split
YAML files while maintaining backward compatibility with single file mode.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/validators/__init__.py

@@ -0,0 +1,36 @@
+# scripts/validators/__init__.py
+"""
+Architecture Validators Package
+===============================
+
+This package contains domain-specific validators for the architecture validation system.
+Each validator module handles a specific category of rules.
+
+Modules:
+    - base: Base classes and helpers (Severity, Violation, ValidationResult)
+    - api_validator: API endpoint rules (API-*)
+    - service_validator: Service layer rules (SVC-*)
+    - model_validator: Model rules (MDL-*)
+    - exception_validator: Exception handling rules (EXC-*)
+    - naming_validator: Naming convention rules (NAM-*)
+    - auth_validator: Auth and multi-tenancy rules (AUTH-*, MT-*)
+    - middleware_validator: Middleware rules (MDW-*)
+    - frontend_validator: Frontend rules (JS-*, TPL-*, FE-*, CSS-*)
+    - language_validator: Language/i18n rules (LANG-*)
+"""
+
+from .base import (
+    BaseValidator,
+    FileResult,
+    Severity,
+    ValidationResult,
+    Violation,
+)
+
+__all__ = [
+    "Severity",
+    "Violation",
+    "FileResult",
+    "ValidationResult",
+    "BaseValidator",
+]