feat: initialize project backend structure and document system specifications across all modules

docs/specs/customer_management/transfer_balance.md

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+---
+title: "Transfer Balance"
+type: OpenSpec
+status: Draft
+domain: Customer Management
+---
+
+# Transfer Balance
+
+## Requirement Definition
+Allows manual transfer of points from a customer/account to another customer/account (External) or between the customer's own accounts (Internal).
+
+## Process Flow
+
+### Pre-Conditions
+- Users must have access rights in the "Transfer Balance" module.
+- Requires Maker-Checker approval.
+
+## Business Rules
+
+### Data Schema
+
+| Field Name | Description | Logic Type | Constraints / Rules |
+|---|---|---|---|
+| Transfer Mode | Internal (self) or External (to another). | Enum | Required. |
+| Transfer Type | Entity type to transfer from (Card, Account, Client). | Enum | Required. |
+| From | Card/Account/CIF Number to transfer from. | String | Required. |
+| To | Card/Account/CIF Number to transfer to. | String | Required. |
+| Pool ID | The pool from which to transfer. | Enum (Lookup) | Required. Must respect "From" entity level. |
+| Store | The store where transaction is logged. | Enum (Lookup) | Required. |
+| Amount to Transfer | Amount. | Decimal | Required. > 0. Defaults to whole pool balance. |
+| Expiry Date | Expiry date of transferred points. | Date | Required. Defaults to source expiry date. |
+| Transaction Code | OLS transaction code. | Enum (Lookup) | Required. |
+| Reason Code | Pre-defined reason for transfer. | Enum (Lookup) | Required. Determines GL posting accounts. |
+| Remarks | Additional remarks. | String (100) | Optional. |
+
+### Execution
+- **Pending/Approve Flow**: Goes to a pending list. Authorised user approves.
+- OLS validates status, block codes, and permissions for both "From" and "To".
+- Rejected if "From" pool balance is insufficient.
+- Execution transfers all linked pools directly from "From" to "To".
+- Logged as a negative Adjustment on "From" and positive Adjustment on "To".
+
+## Post-Conditions
+- Pool balances updated.
+
+## Exception Flow
+- Insufficient balance, TP validation failures, or input errors block the action.