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>

alembic/versions/zc2m3n4o5p6q7_add_platform_modules_table.py

@@ -0,0 +1,142 @@
+"""Add platform modules table
+
+Revision ID: zc2m3n4o5p6q7
+Revises: zb1l2m3n4o5p6
+Create Date: 2026-01-26
+
+Adds platform_modules junction table for tracking module enablement per platform:
+- Auditability: Track when modules were enabled/disabled and by whom
+- Configuration: Per-module settings specific to each platform
+- State tracking: Explicit enabled/disabled states with timestamps
+
+This replaces the simpler Platform.settings["enabled_modules"] JSON approach
+for better auditability and query capabilities.
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = "zc2m3n4o5p6q7"
+down_revision = "zb1l2m3n4o5p6"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # Create platform_modules table
+    op.create_table(
+        "platform_modules",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column(
+            "platform_id",
+            sa.Integer(),
+            nullable=False,
+            comment="Platform this module configuration belongs to",
+        ),
+        sa.Column(
+            "module_code",
+            sa.String(50),
+            nullable=False,
+            comment="Module code (e.g., 'billing', 'inventory', 'orders')",
+        ),
+        sa.Column(
+            "is_enabled",
+            sa.Boolean(),
+            nullable=False,
+            server_default="true",
+            comment="Whether this module is currently enabled for the platform",
+        ),
+        sa.Column(
+            "enabled_at",
+            sa.DateTime(timezone=True),
+            nullable=True,
+            comment="When the module was last enabled",
+        ),
+        sa.Column(
+            "enabled_by_user_id",
+            sa.Integer(),
+            nullable=True,
+            comment="User who enabled the module",
+        ),
+        sa.Column(
+            "disabled_at",
+            sa.DateTime(timezone=True),
+            nullable=True,
+            comment="When the module was last disabled",
+        ),
+        sa.Column(
+            "disabled_by_user_id",
+            sa.Integer(),
+            nullable=True,
+            comment="User who disabled the module",
+        ),
+        sa.Column(
+            "config",
+            sa.JSON(),
+            nullable=False,
+            server_default="{}",
+            comment="Module-specific configuration for this platform",
+        ),
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            nullable=False,
+            server_default=sa.func.now(),
+        ),
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            nullable=False,
+            server_default=sa.func.now(),
+            onupdate=sa.func.now(),
+        ),
+        # Primary key
+        sa.PrimaryKeyConstraint("id"),
+        # Foreign keys
+        sa.ForeignKeyConstraint(
+            ["platform_id"],
+            ["platforms.id"],
+            ondelete="CASCADE",
+        ),
+        sa.ForeignKeyConstraint(
+            ["enabled_by_user_id"],
+            ["users.id"],
+            ondelete="SET NULL",
+        ),
+        sa.ForeignKeyConstraint(
+            ["disabled_by_user_id"],
+            ["users.id"],
+            ondelete="SET NULL",
+        ),
+        # Unique constraint - one config per platform/module pair
+        sa.UniqueConstraint("platform_id", "module_code", name="uq_platform_module"),
+    )
+
+    # Create indexes for performance
+    op.create_index(
+        "idx_platform_module_platform_id",
+        "platform_modules",
+        ["platform_id"],
+    )
+    op.create_index(
+        "idx_platform_module_code",
+        "platform_modules",
+        ["module_code"],
+    )
+    op.create_index(
+        "idx_platform_module_enabled",
+        "platform_modules",
+        ["platform_id", "is_enabled"],
+    )
+
+
+def downgrade() -> None:
+    # Drop indexes
+    op.drop_index("idx_platform_module_enabled", table_name="platform_modules")
+    op.drop_index("idx_platform_module_code", table_name="platform_modules")
+    op.drop_index("idx_platform_module_platform_id", table_name="platform_modules")
+
+    # Drop table
+    op.drop_table("platform_modules")