feat: add module config and migrations auto-discovery infrastructure

Add self-contained configuration and migrations support for modules:

Config auto-discovery (app/modules/config.py):
- Modules can have config.py with Pydantic Settings
- Environment variables prefixed with MODULE_NAME_
- Auto-discovered via get_module_config()

Migrations auto-discovery:
- Each module has migrations/versions/ directory
- Alembic discovers module migrations automatically
- Naming convention: {module}_{seq}_{description}.py

New architecture rules (MOD-013 to MOD-015):
- MOD-013: config.py should export config/config_class
- MOD-014: Migrations must follow naming convention
- MOD-015: Migrations directory must have __init__.py

Created for all 11 self-contained modules:
- config.py placeholder files
- migrations/ directories with __init__.py files

Added core and tenancy module definitions for completeness.

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

app/modules/core/__init__.py

@@ -0,0 +1,11 @@
+# app/modules/core/__init__.py
+"""
+Core Platform module.
+
+Provides dashboard, settings, and profile management.
+This is a core module that cannot be disabled.
+"""
+
+from app.modules.core.definition import core_module
+
+__all__ = ["core_module"]

app/modules/core/definition.py

@@ -0,0 +1,39 @@
+# app/modules/core/definition.py
+"""
+Core Platform module definition.
+
+Dashboard, settings, and profile management.
+Required for basic operation - cannot be disabled.
+"""
+
+from app.modules.base import ModuleDefinition
+from models.database.admin_menu_config import FrontendType
+
+core_module = ModuleDefinition(
+    code="core",
+    name="Core Platform",
+    description="Dashboard, settings, and profile management. Required for basic operation.",
+    version="1.0.0",
+    is_core=True,
+    features=[
+        "dashboard",
+        "settings",
+        "profile",
+    ],
+    menu_items={
+        FrontendType.ADMIN: [
+            "dashboard",
+            "settings",
+            "email-templates",
+            "my-menu",
+        ],
+        FrontendType.VENDOR: [
+            "dashboard",
+            "profile",
+            "settings",
+            "email-templates",
+        ],
+    },
+)
+
+__all__ = ["core_module"]