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

docs/specs/reward_campaign/external_transaction_code.md

@@ -0,0 +1,33 @@
+---
+title: "External Transaction Code"
+type: OpenSpec
+status: Draft
+domain: Reward Campaign Management
+---
+
+# External Transaction Code
+
+## Requirement Definition
+Maps incoming transaction codes from external systems (e.g., Card System) to OLS Transaction Codes.
+
+## Process Flow
+
+### Pre-Conditions
+- Users must have access rights in the module.
+
+## Business Rules
+
+### Data Schema
+
+| Field Name | Description | Logic Type | Constraints / Rules |
+|---|---|---|---|
+| External Transaction Code | Source System Transaction Code. | String (10) | Required. |
+| Description | Description for reference. | String (30) | Required. |
+
+### Execution
+- An External System TC is the first key used to locate the corresponding OLS TC for processing.
+- Each External TC must be mapped to an OLS TC.
+- Supports Maker-Checker approval workflow (Pending -> Active).
+
+## Exception Flow
+- N/A