Add comprehensive interface documentation (INTERFACES.md)

[Copilot]

Documents all data structures and APIs across the FraudDetect codebase in a centralized reference.

Documentation Coverage

• Backend interfaces: Pydantic schemas for users, checks, agents, and admin operations
• Database models: SQLAlchemy ORM mappings for User, Bank, and Cheque entities
• Frontend interfaces: TypeScript definitions for authentication, check management, and admin panels
• State management: Zustand store interfaces for auth and agent sessions
• API contracts: Service layer interfaces and request/response types
• Component props: React component interface definitions

Structure

Organized by architectural layer with:

• Code snippets showing actual interface definitions
• Data flow diagrams for main user journeys (auth, check processing, admin operations)
• Security model documentation (Clerk integration, role-based access)
• Usage examples for common patterns

Example interface from the docs:

export interface AgentDashboardResponse {
    cheques_meme_banque: ChequeItem[];      // Internal bank checks
    cheques_autre_banque: ChequeItem[];     // External bank checks
    agentName: string;
    agentEmail: string;
    agentBankId: number;
}

The documentation reflects current mixed naming conventions (French/English) as they exist in the codebase.

Original prompt

decrire les interfaces dans cette branche du projet

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