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

docs/specs/reward_campaign/campaign_structure.md

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+---
+title: "Campaign Structure"
+type: OpenSpec
+status: Draft
+domain: Reward Campaign Management
+---
+
+# Campaign Structure
+
+## Requirement Definition
+Defines the conceptual structure and mechanics of how reward campaigns operate in OLS, managing the issuance and redemption of various reward types (Points, Cash Rebates, eCoupons, Lucky Draw chances).
+
+## Process Flow
+
+### Pre-Conditions
+- N/A (Core concepts)
+
+## Business Rules
+
+### Types of Campaign Mechanics
+1. **Award on Every Transaction**: Rewards are determined and given at the time the transaction is processed (real-time or batch).
+2. **Accumulate Then Award**: Rewards depend on cumulative criteria (e.g., total spend over a month). Transactions update Counters, and at the end of the period, a separate process extracts the Counter value to determine the award.
+3. **Auto-redemption Campaigns**: Awarded quantities (e.g., Cash Rebates) are immediately "redeemed" and sent to an external system (like a Core Banking system) to credit the customer's account.
+
+### Reward Pool Structure & Deduction
+- Earnings are tracked in "Pools" by reward type.
+- Pools belong to Loyalty Accounts (or specific Accounts/Cards).
+- Stored value is tracked in Buckets segregated by Expiry Date and Account Type.
+- **Redemption Sequence**: 
+  - Deducted in ascending Expiry Date (earliest expiring first).
+  - If identical expiry dates, sorted by a pre-configured Account Type priority sequence.
+
+### Counters
+- A Counter tracks a quantity (e.g., spend amount, transaction frequency) over a defined time period (Bucket).
+- Entities tracked: Customer, Account, Card, Store, Chain, etc.
+- Quantities tracked: Gross Amount, Nett Amount, Points, Transaction Count, Custom Quantities.
+- Counter Periods: Days, Weeks, Months, Quarters, Years, Fixed Date, No Expiry, Days/Months/Quarters from Account Open Date.
+
+## Exception Flow
+- N/A