feat: add paypal refunds diagram

docs/arch-diagrams/automatic-refunds.mmd

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+sequenceDiagram
+    actor User as User
+    participant LMS as LMS
+    participant CC
+    participant CoCo
+    participant AWS as AWS EventBridge
+    participant PSP as Stripe/PayPal
+
+    note over User,LMS: User Unenrolls from Course
+    User ->> LMS: Click on Gear CTA -> Click "Unenroll" -> Answer Question
+    LMS ->> LMS: Determines Which System to Hit
+    LMS ->> LMS: Checks Source System of Enrollment Attributes<br>(COMMERCE_COORDINATOR_REFUND_SOURCE_SYSTEMS)
+
+    critical Create Refund
+        LMS ->> CC: Hits RefundView() Endpoint
+        activate CC
+        CC ->> CoCo: Create ReturnItemDraft
+        activate CoCo
+        CoCo ->> CoCo: Creates LineItemReturnItem
+        CoCo ->> CoCo: Shipment State Transitions to "Returned"
+        CoCo ->> CoCo: Payment State Transitions to "Initial"
+        CoCo -->> CC: Response
+        deactivate CoCo
+        CC -->> LMS: Response
+        deactivate CC
+    end
+
+    CoCo ->> AWS: Emits LineItemReturnItem Subscription Message
+    AWS ->> CC: Hits OrderReturnedView() Endpoint
+    CC ->> CC: Receives message from CoCo via AWS EventBridge <br> with details of ReturnItem
+    CC ->> CC: Triggers fulfill_order_returned_signal<br> worker_task
+    CC ->> PSP: Issue Credit
+    activate PSP
+    PSP -->> CC: Response
+    deactivate PSP
+    CC ->> CoCo: Add Refund Transaction to Payment Obj
+    activate CoCo
+    CoCo -->> CC: Response
+    deactivate CoCo
+    CC ->> CoCo: Update Refund Status
+    activate CoCo
+    CoCo -->> CC: Response
+    deactivate CoCo
+    note over User,LMS: LMS Unenrolls User
+    LMS -->> User: Removes Course from Dashboard

docs/arch-diagrams/manual-refunds.mmd

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+sequenceDiagram
+    actor Support
+    participant CoCo
+    participant AWS EventBridge
+    participant Commerce Coordinator
+    participant PSP as Stripe/PayPal
+    Support->>CoCo: Create ReturnItem
+    CoCo->>AWS EventBridge: Emits LineItemReturnItem Subscription Message
+    AWS EventBridge->>Commerce Coordinator: Hits OrderReturnedView() Endpoint
+    Commerce Coordinator->>Commerce Coordinator: Receives message from CoCo via AWS EventBridge<br> with details of the ReturnItem
+    Commerce Coordinator->>Commerce Coordinator: Triggers fulfill_order_returned_signal<br> worker task
+    Commerce Coordinator->>PSP: Issue Credit
+    activate PSP
+    PSP-->>Commerce Coordinator: Response
+    deactivate PSP
+    Commerce Coordinator->>CoCo: Add Refund Transaction to Payment Obj
+    activate CoCo
+    CoCo-->>Commerce Coordinator: Response
+    deactivate CoCo
+    Commerce Coordinator->>CoCo: Update Refund Status
+    activate CoCo
+    CoCo-->>Commerce Coordinator: Response
+    deactivate CoCo

docs/arch-diagrams/webhook-refunds.mmd

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+sequenceDiagram
+    actor Support
+    participant PSP as Stripe/PayPal
+    participant CC as Commerce Coordinator
+    participant CoCo
+    note over Support, PSP: Support Issues Refund<br>from PSP Dashboard
+    Support ->> PSP: Issue Refund
+    activate PSP
+    PSP -->> PSP: Issues Refund to User
+    PSP -->> PSP: Triggers refund Webhook
+    PSP ->> CC: Hits WebhookView() Endpoint
+    deactivate PSP
+    activate CC
+    CC -->> CC: Sends payment_refunded_signal<br> signal
+    CC -->> CC: Triggers refund_from_stripe_task<br> worker task
+    CC ->> CoCo: Adds Refund Transaction<br> to Payment Obj
+    deactivate CC