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

docs/specs/reward_campaign/campaign_rule_criteria.md

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+---
+title: "Campaign Rule Criteria"
+type: OpenSpec
+status: Draft
+domain: Reward Campaign Management
+---
+
+# Campaign Rule Criteria
+
+## Requirement Definition
+Defines the conditions a transaction must meet to trigger a Campaign Rule. Built using a drag-and-drop Query Builder interface.
+
+## Process Flow
+
+### Pre-Conditions
+- Rule must be created.
+
+## Business Rules
+
+### Data Schema
+Criteria are categorized into: Customer, Account, Transaction, Attribute, Counter, Merchant.
+
+#### Operators
+| Data Type | Operators | Logic Type / Details |
+|---|---|---|
+| String / Lookup | Is in, Is not in, Contains, Equal to, Not equal to, Starts with, Ends with, Is null, Is not null. | Validates against provided text or list of values. |
+| Number | Equal, Not equal, Less than, Less/equal, Greater, Greater/equal, Between, Null, Not null. | Standard numerical comparison. |
+| Date | On or before, On or after, Fixed date, Between date range, Between period from N. | Complex date logic (e.g. comparing Day/Month regardless of year, comparing "3 months ago"). |
+| Day of week | Is the day of week. | Monday-Sunday. |
+| Time | Is between. | Time-of-day comparison (00:00 - 23:59). |
+| Boolean | Is. | True / False. |
+
+### Execution
+- Supports AND and OR logic grouping.
+- A single rule can have multiple groups, but inter-group logic must be consistent (all ANDs or all ORs).
+- NOT toggles support exclusion.
+- All criteria defined in the rule must evaluate to true (for AND) or at least one (for OR) to trigger the Formula execution.
+
+## Exception Flow
+- Validation failure means the rule is not triggered (proceeds to next rule in Execution Sequence).