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/middleware.yaml

@@ -0,0 +1,22 @@
+# Architecture Rules - Middleware Rules
+# Rules for middleware/**/*.py files
+
+middleware_rules:
+
+  - id: "MDW-001"
+    name: "Middleware files use simple nouns without _middleware suffix"
+    severity: "warning"
+    description: |
+      Middleware files should be named with simple nouns (auth.py, not auth_middleware.py)
+    pattern:
+      file_pattern: "middleware/**/*.py"
+      check: "middleware_naming"
+
+  - id: "MDW-002"
+    name: "Vendor context must be injected for vendor/shop routes"
+    severity: "error"
+    description: |
+      Vendor context middleware must set request.state.vendor_id and request.state.vendor
+    pattern:
+      file_pattern: "middleware/vendor_context.py"
+      required: true