feat: implement three-tier module classification and framework layer

Module Classification:
- Core (4): core, tenancy, cms, customers - always enabled
- Optional (7): payments, billing, inventory, orders, marketplace, analytics, messaging
- Internal (2): dev-tools, monitoring - admin-only

Key Changes:
- Rename platform-admin module to tenancy
- Promote CMS and Customers to core modules
- Create new payments module (gateway abstractions)
- Add billing→payments and orders→payments dependencies
- Mark dev-tools and monitoring as internal modules

New Infrastructure:
- app/modules/events.py: Module event bus (ENABLED, DISABLED, STARTUP, SHUTDOWN)
- app/modules/migrations.py: Module-specific migration discovery
- app/core/observability.py: Health checks, Prometheus metrics, Sentry integration

Enhanced ModuleDefinition:
- version, is_internal, permissions
- config_schema, default_config
- migrations_path
- Lifecycle hooks: on_enable, on_disable, on_startup, health_check

New Registry Functions:
- get_optional_module_codes(), get_internal_module_codes()
- is_core_module(), is_internal_module()
- get_modules_by_tier(), get_module_tier()

Migrations:
- zc*: Rename platform-admin to tenancy
- zd*: Ensure CMS and Customers enabled for all platforms

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

app/modules/payments/schemas/__init__.py

@@ -0,0 +1,93 @@
+# app/modules/payments/schemas/__init__.py
+"""
+Payments module Pydantic schemas.
+"""
+
+from pydantic import BaseModel, Field
+from datetime import datetime
+from typing import Any
+
+
+class PaymentRequest(BaseModel):
+    """Request to process a payment."""
+
+    amount: int = Field(..., gt=0, description="Amount in cents")
+    currency: str = Field(default="EUR", max_length=3)
+    payment_method_id: str | None = None
+    gateway: str = Field(default="stripe")
+    description: str | None = None
+    metadata: dict[str, Any] = Field(default_factory=dict)
+
+
+class PaymentResponse(BaseModel):
+    """Response from a payment operation."""
+
+    success: bool
+    transaction_id: str | None = None
+    gateway: str | None = None
+    status: str
+    amount: int
+    currency: str
+    error_message: str | None = None
+    created_at: datetime | None = None
+
+
+class RefundRequest(BaseModel):
+    """Request to issue a refund."""
+
+    transaction_id: str
+    amount: int | None = Field(None, gt=0, description="Amount in cents, None for full refund")
+    reason: str | None = None
+
+
+class RefundResponse(BaseModel):
+    """Response from a refund operation."""
+
+    success: bool
+    refund_id: str | None = None
+    transaction_id: str
+    amount: int
+    status: str
+    error_message: str | None = None
+
+
+class PaymentMethodCreate(BaseModel):
+    """Request to create a payment method."""
+
+    gateway: str = "stripe"
+    token: str  # Gateway-specific token
+    is_default: bool = False
+
+
+class PaymentMethodResponse(BaseModel):
+    """Response for a payment method."""
+
+    id: str
+    gateway: str
+    type: str  # card, bank_account, etc.
+    last4: str | None = None
+    is_default: bool
+    created_at: datetime
+
+
+class GatewayResponse(BaseModel):
+    """Response for gateway info."""
+
+    code: str
+    name: str
+    status: str
+    enabled: bool
+    supports_refunds: bool
+    supports_recurring: bool
+    supported_currencies: list[str]
+
+
+__all__ = [
+    "PaymentRequest",
+    "PaymentResponse",
+    "RefundRequest",
+    "RefundResponse",
+    "PaymentMethodCreate",
+    "PaymentMethodResponse",
+    "GatewayResponse",
+]