Implement validateUniqueness and validateBusinessRule methods

[Copilot]

Two core validation methods in validator.ts were empty stubs that always returned true. This PR implements their actual logic.

Changes

validateUniqueness

• Queries database via context.api.count() to detect duplicate values
• Supports single field (field) and composite (fields) uniqueness constraints
• Excludes current record on updates using { _id: { $ne: previousRecord._id } }
• Returns early on null values (nothing to validate)
• Applies scope conditions when specified

validateBusinessRule

• Evaluates all_of (AND), any_of (OR), and then_require constraint logic
• Delegates to existing evaluateCondition method for field comparisons
• Expression constraints remain stubbed (requires safe evaluator)

Helper

• extractFieldsFromCondition: recursively extracts field names from nested conditions for scope filtering

Example Usage

const uniqueRule: UniquenessValidationRule = {
  name: 'unique_email',
  type: 'unique',
  field: 'email',
  message: 'Email already exists',
};

const context: ValidationContext = {
  record: { email: 'test@example.com' },
  operation: 'create',
  api: mockApi,
  metadata: { objectName: 'user' },
};

const result = await validator.validate([uniqueRule], context);
// Queries: count('user', { email: 'test@example.com' })
// Returns: { valid: false } if count > 0

Notes

• Case-insensitive string comparison requires driver-specific implementation (documented in code)
• Gracefully degrades when context.api is unavailable (returns valid: true)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Feature: Implement missing Validator logic (Uniqueness & Business Rules)</issue_title>
<issue_description>## Problem
In packages/foundation/core/src/validator.ts, key validation methods are currently empty stubs:

• validateUniqueness: Returns true without checking the database.
• validateBusinessRule: Returns true without evaluating expressions.

Goal

• Implement validateUniqueness by checking the database count for the field value.
• Implement basic validateBusinessRule logic.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Feature: Implement missing Validator logic (Uniqueness & Business Rules) #22

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