feat: implement typed frappe api client and secure auth poc (#18)

poc-frappe-api/.gitignore

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+node_modules/
+dist/
+coverage/
+.env

poc-frappe-api/README.md

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+# Typed Frappe API Client (PoC)
+
+This directory contains the Proof of Concept (PoC) for Issue #18: **Typed Frappe API Client and Secure Authentication Layer**.
+
+## Overview
+
+This module provides a centralized, type-safe way to communicate with the Frappe LMS backend. It focuses on:
+1.  **Secure Credential Handling**: Abstract interface for `api_key:api_secret` storage.
+2.  **Request Interceptors**: Automatic injection of Authorization headers.
+3.  **Response Interceptors**: Centralized handling of `401/403` unauthorized errors.
+4.  **TypeScript Models**: Strongly typed DocTypes (Course, Lesson, User).
+
+## Architecture
+
+```mermaid
+graph LR
+    App[React Native UI] --> Client[FrappeClient]
+    Client --> Axios[Axios Instance]
+    Axios --> Interceptor[Auth Interceptor]
+    Interceptor --> Storage[AuthService / Keychain]
+    Axios --> API[Frappe REST API]
+```
+
+## Setup & Testing
+
+1.  Install dependencies:
+    ```bash
+    cd poc-frappe-api
+    npm install
+    ```
+2.  Run unit tests:
+    ```bash
+    npm test
+    ```
+
+## Key Files
+- `src/models/index.ts`: TypeScript interfaces for LMS resources.
+- `src/AuthService.ts`: Credential management logic.
+- `src/FrappeClient.ts`: Main API client with interceptors.
+- `tests/FrappeClient.test.ts`: Interceptor and error handling tests.

poc-frappe-api/jest.config.js

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+const { createDefaultPreset } = require("ts-jest");
+
+const tsJestTransformCfg = createDefaultPreset().transform;
+
+/** @type {import("jest").Config} **/
+module.exports = {
+  testEnvironment: "node",
+  transform: {
+    ...tsJestTransformCfg,
+  },
+};