feat(examples): add microservices platform architecture, rules, and sample services

- Add `architecture.yml` describing billing/identity contexts, services, library, and interactions
- Add Pacta rules enforcing service/layer dependency constraints
- Add shared `Money` utility plus minimal billing and identity service scaffolding

Author: akhundMurad

examples/microservices-platform/architecture.yml

@@ -0,0 +1,85 @@
+version: 2
+
+system:
+  id: microservices-platform
+  name: Microservices Platform
+
+contexts:
+  billing:
+    name: Billing Context
+    description: Handles invoicing, payments, and billing operations
+  identity:
+    name: Identity Context
+    description: User authentication and authorization
+
+containers:
+  billing-service:
+    kind: service
+    name: Billing Service
+    context: billing
+    code:
+      roots:
+        - services/billing
+      layers:
+        api:
+          name: API Layer
+          patterns:
+            - services/billing/api/**
+        domain:
+          name: Domain Layer
+          patterns:
+            - services/billing/domain/**
+    contains:
+      invoice-module:
+        kind: module
+        name: Invoice Module
+        code:
+          roots:
+            - services/billing/domain/invoice
+          layers:
+            model:
+              name: Domain Model
+              patterns:
+                - services/billing/domain/invoice/model/**
+            repo:
+              name: Repository
+              patterns:
+                - services/billing/domain/invoice/repo/**
+
+  identity-service:
+    kind: service
+    name: Identity Service
+    context: identity
+    code:
+      roots:
+        - services/identity
+      layers:
+        domain:
+          name: Domain Layer
+          patterns:
+            - services/identity/core/**
+        infra:
+          name: Infrastructure Layer
+          patterns:
+            - services/identity/db/**
+
+  shared-utils:
+    kind: library
+    name: Shared Utilities
+    code:
+      roots:
+        - libs/shared
+
+interactions:
+  - from: billing-service
+    to: identity-service
+    protocol: http
+    description: Billing verifies user identity
+  - from: billing-service
+    to: shared-utils
+    protocol: import
+    description: Billing uses shared utilities
+  - from: identity-service
+    to: shared-utils
+    protocol: import
+    description: Identity uses shared utilities

examples/microservices-platform/libs/shared/money.py

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+class Money:
+    def __init__(self, amount: float):
+        self.amount = amount

examples/microservices-platform/rules.pacta.yml

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+rules:
+  - id: no-cross-service-domain-deps
+    name: Domain must not depend on other services
+    severity: error
+    target: dependency
+    action: forbid
+    when:
+      all:
+        - from.service != to.service
+        - from.layer == domain
+    message: Domain code must not depend on another service
+
+  - id: library-no-service-deps
+    name: Libraries must be independent of services
+    severity: error
+    target: dependency
+    action: forbid
+    when:
+      all:
+        - from.kind == library
+        - to.kind == service
+    message: Library code must not import service code
+
+  - id: no-infra-to-api
+    name: Infrastructure must not depend on API layer
+    severity: error
+    target: dependency
+    action: forbid
+    when:
+      all:
+        - from.layer == infra
+        - to.layer == api
+    message: Infrastructure layer must not depend on the API layer

examples/microservices-platform/services/billing/api/routes.py

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+from services.billing.domain.invoice.model.invoice import Invoice
+from services.identity.core.auth import verify_token
+
+
+def create_invoice(request):
+    verify_token(request.token)
+    return Invoice.create(request.data)

examples/microservices-platform/services/billing/domain/invoice/model/invoice.py

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+from libs.shared.money import Money
+
+
+class Invoice:
+    def __init__(self, amount: "Money"):
+        self.amount = amount
+
+    @classmethod
+    def create(cls, data: dict) -> "Invoice":
+        return cls(amount=Money(data["amount"]))

examples/microservices-platform/services/billing/domain/invoice/repo/invoice_repo.py

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+from services.billing.domain.invoice.model.invoice import Invoice
+
+
+class InvoiceRepository:
+    def save(self, invoice: Invoice) -> None:
+        pass
+
+    def find_by_id(self, invoice_id: str) -> Invoice | None:
+        pass

examples/microservices-platform/services/identity/core/auth.py

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+def verify_token(token: str) -> bool:
+    return token is not None

examples/microservices-platform/services/identity/db/user_store.py

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+class UserStore:
+    def find_by_email(self, email: str) -> dict | None:
+        pass