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>

.architecture-rules/_main.yaml

@@ -0,0 +1,102 @@
+# Architecture Rules - Main Configuration
+# This file defines core settings and includes domain-specific rule files.
+
+version: "2.0"
+project: "letzshop-product-import"
+description: "Comprehensive architectural rules for multi-tenant e-commerce platform"
+
+# ============================================================================
+# CORE ARCHITECTURAL PRINCIPLES
+# ============================================================================
+
+principles:
+  - name: "Separation of Concerns"
+    description: "API endpoints should only handle HTTP concerns. Business logic belongs in services."
+
+  - name: "Layered Architecture"
+    description: "Routes → Services → Models. Each layer has specific responsibilities."
+
+  - name: "Type Safety"
+    description: "Use Pydantic models for request/response validation. Use SQLAlchemy models for database."
+
+  - name: "Proper Exception Handling"
+    description: "Services throw domain exceptions. Global handler converts to HTTP responses. Endpoints do NOT catch or raise HTTPException."
+
+  - name: "Multi-Tenancy"
+    description: "All queries must be scoped to vendor_id. No cross-vendor data access."
+
+  - name: "Consistent Naming"
+    description: "API files: plural, Services: singular+service, Models: singular"
+
+# ============================================================================
+# RULE FILE INCLUDES
+# ============================================================================
+
+includes:
+  - api.yaml
+  - service.yaml
+  - model.yaml
+  - exception.yaml
+  - naming.yaml
+  - auth.yaml
+  - middleware.yaml
+  - frontend.yaml
+  - language.yaml
+  - quality.yaml
+
+# ============================================================================
+# VALIDATION SEVERITY LEVELS
+# ============================================================================
+
+severity_levels:
+  error:
+    description: "Critical architectural violation - must be fixed"
+    exit_code: 1
+
+  warning:
+    description: "Pattern deviation - should be fixed"
+    exit_code: 0
+
+  info:
+    description: "Suggestion for improvement"
+    exit_code: 0
+
+# ============================================================================
+# IGNORED PATTERNS
+# ============================================================================
+
+ignore:
+  files:
+    - "**/*_test.py"
+    - "**/test_*.py"
+    - "**/__pycache__/**"
+    - "**/migrations/**"
+    - "**/alembic/versions/**"
+    - "**/node_modules/**"
+    - "**/.venv/**"
+    - "**/venv/**"
+    - ".venv/**"
+    - "venv/**"
+    - "**/build/**"
+    - "**/dist/**"
+
+  patterns:
+    # Allow HTTPException in specific files
+    - file: "app/core/exceptions.py"
+      pattern: "HTTPException"
+      reason: "Exception handling utilities"
+
+    - file: "app/exceptions/handler.py"
+      pattern: "HTTPException"
+      reason: "Exception handler converts to HTTP"
+
+# ============================================================================
+# DOCUMENTATION
+# ============================================================================
+
+documentation:
+  architecture: "docs/architecture/overview.md"
+  backend: "docs/backend/overview.md"
+  frontend: "docs/frontend/overview.md"
+  contributing: "docs/development/contributing.md"
+  code_quality: "docs/development/code-quality.md"