feat: complete modular platform architecture (Phases 1-5)

Phase 1 - Vendor Router Integration:
- Wire up vendor module routers in app/api/v1/vendor/__init__.py
- Use lazy imports via __getattr__ to avoid circular dependencies

Phase 2 - Extract Remaining Modules:
- Create 6 new module directories: customers, cms, analytics, messaging,
  dev_tools, monitoring
- Each module has definition.py and route wrappers
- Update registry to import from extracted modules

Phase 3 - Database Table Migration:
- Add PlatformModule junction table for auditable module tracking
- Add migration zc2m3n4o5p6q7_add_platform_modules_table.py
- Add modules relationship to Platform model
- Update ModuleService with JSON-to-junction-table migration

Phase 4 - Module-Specific Configuration UI:
- Add /api/v1/admin/module-config/* endpoints
- Add module-config.html template and JS

Phase 5 - Integration Tests:
- Add tests/fixtures/module_fixtures.py
- Add tests/integration/api/v1/admin/test_modules.py
- Add tests/integration/api/v1/modules/test_module_access.py

Architecture fixes:
- Fix JS-003 errors: use ...data() directly in Alpine components
- Fix JS-005 warnings: add init() guards to prevent duplicate init
- Fix API-001 errors: add MenuActionResponse Pydantic model
- Add FE-008 noqa for dynamic number input in template

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

tests/fixtures/module_fixtures.py

@@ -0,0 +1,159 @@
+# tests/fixtures/module_fixtures.py
+"""
+Module system test fixtures.
+
+Provides fixtures for testing platform module enablement, configuration,
+and access control.
+"""
+
+import uuid
+from datetime import datetime, timezone
+
+import pytest
+
+from models.database.platform import Platform
+from models.database.platform_module import PlatformModule
+
+
+@pytest.fixture
+def platform_with_modules(db, test_super_admin):
+    """Create a test platform with specific modules enabled."""
+    unique_id = str(uuid.uuid4())[:8]
+    platform = Platform(
+        code=f"modtest_{unique_id}",
+        name=f"Module Test Platform {unique_id}",
+        description="A test platform with module configuration",
+        path_prefix=f"modtest{unique_id}",
+        is_active=True,
+        is_public=True,
+        default_language="en",
+        supported_languages=["en", "fr"],
+    )
+    db.add(platform)
+    db.flush()
+
+    # Enable specific modules via junction table
+    enabled_modules = ["billing", "inventory", "orders"]
+    for module_code in enabled_modules:
+        pm = PlatformModule(
+            platform_id=platform.id,
+            module_code=module_code,
+            is_enabled=True,
+            enabled_at=datetime.now(timezone.utc),
+            enabled_by_user_id=test_super_admin.id,
+            config={},
+        )
+        db.add(pm)
+
+    # Add a disabled module
+    pm_disabled = PlatformModule(
+        platform_id=platform.id,
+        module_code="marketplace",
+        is_enabled=False,
+        disabled_at=datetime.now(timezone.utc),
+        disabled_by_user_id=test_super_admin.id,
+        config={},
+    )
+    db.add(pm_disabled)
+
+    db.commit()
+    db.refresh(platform)
+    return platform
+
+
+@pytest.fixture
+def platform_with_config(db, test_super_admin):
+    """Create a test platform with module configuration."""
+    unique_id = str(uuid.uuid4())[:8]
+    platform = Platform(
+        code=f"cfgtest_{unique_id}",
+        name=f"Config Test Platform {unique_id}",
+        description="A test platform with module config",
+        path_prefix=f"cfgtest{unique_id}",
+        is_active=True,
+        is_public=True,
+        default_language="en",
+        supported_languages=["en"],
+    )
+    db.add(platform)
+    db.flush()
+
+    # Add module with configuration
+    pm = PlatformModule(
+        platform_id=platform.id,
+        module_code="billing",
+        is_enabled=True,
+        enabled_at=datetime.now(timezone.utc),
+        enabled_by_user_id=test_super_admin.id,
+        config={
+            "stripe_mode": "test",
+            "default_trial_days": 30,
+            "allow_free_tier": True,
+        },
+    )
+    db.add(pm)
+
+    # Add inventory module with config
+    pm_inv = PlatformModule(
+        platform_id=platform.id,
+        module_code="inventory",
+        is_enabled=True,
+        enabled_at=datetime.now(timezone.utc),
+        enabled_by_user_id=test_super_admin.id,
+        config={
+            "low_stock_threshold": 5,
+            "enable_locations": True,
+        },
+    )
+    db.add(pm_inv)
+
+    db.commit()
+    db.refresh(platform)
+    return platform
+
+
+@pytest.fixture
+def platform_all_modules_disabled(db, test_super_admin):
+    """Create a test platform with all optional modules disabled."""
+    unique_id = str(uuid.uuid4())[:8]
+    platform = Platform(
+        code=f"nomod_{unique_id}",
+        name=f"No Modules Platform {unique_id}",
+        description="A test platform with minimal modules",
+        path_prefix=f"nomod{unique_id}",
+        is_active=True,
+        is_public=True,
+        default_language="en",
+        supported_languages=["en"],
+        settings={"enabled_modules": []},  # Legacy format for testing
+    )
+    db.add(platform)
+    db.commit()
+    db.refresh(platform)
+    return platform
+
+
+@pytest.fixture
+def module_factory(db, test_super_admin):
+    """Factory for creating PlatformModule records."""
+    def _create_module(
+        platform_id: int,
+        module_code: str,
+        is_enabled: bool = True,
+        config: dict | None = None,
+    ):
+        pm = PlatformModule(
+            platform_id=platform_id,
+            module_code=module_code,
+            is_enabled=is_enabled,
+            enabled_at=datetime.now(timezone.utc) if is_enabled else None,
+            enabled_by_user_id=test_super_admin.id if is_enabled else None,
+            disabled_at=None if is_enabled else datetime.now(timezone.utc),
+            disabled_by_user_id=None if is_enabled else test_super_admin.id,
+            config=config or {},
+        )
+        db.add(pm)
+        db.commit()
+        db.refresh(pm)
+        return pm
+    return _create_module