feat: 프로젝트 초기 구조 설정

- PyQt5 POS 판매 조회 GUI (Phase 1 완료)
- Flask API 서버 스켈레톤 (Phase 2 준비)
- SQLite 마일리지 DB 스키마 설계
- 프로젝트 문서 및 README 추가
- 기본 디렉터리 구조 생성

Phase 1: POS 판매 내역 조회 GUI 완료
Phase 2: QR 토큰 생성 및 마일리지 적립 (예정)
Phase 3: 카카오 로그인 연동 (예정)
Phase 4: 마일리지 시스템 완성 (예정)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

backend/db/mileage_schema.sql

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+-- SQLite 마일리지 데이터베이스 스키마
+-- pharmacy-pos-qr-system/backend/db/mileage_schema.sql
+
+-- 1. 사용자 테이블 (카카오 로그인 계정)
+CREATE TABLE IF NOT EXISTS users (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    nickname VARCHAR(100),
+    profile_image_url VARCHAR(500),
+    email VARCHAR(200),
+    is_email_verified BOOLEAN DEFAULT FALSE,
+    phone VARCHAR(20),
+    mileage_balance INTEGER DEFAULT 0,
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
+);
+
+-- 2. 외부 로그인 매핑 테이블
+CREATE TABLE IF NOT EXISTS customer_identities (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id INTEGER NOT NULL,
+    provider VARCHAR(20) NOT NULL,
+    provider_user_id VARCHAR(100) NOT NULL,
+    provider_data TEXT,
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (user_id) REFERENCES users(id),
+    UNIQUE(provider, provider_user_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_identities_user ON customer_identities(user_id);
+
+-- 3. 영수증 QR 토큰 테이블
+CREATE TABLE IF NOT EXISTS claim_tokens (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    transaction_id VARCHAR(20) NOT NULL,
+    pharmacy_id VARCHAR(20),
+    token_hash VARCHAR(64) NOT NULL,
+    total_amount INTEGER NOT NULL,
+    claimable_points INTEGER NOT NULL,
+    expires_at DATETIME NOT NULL,
+    claimed_at DATETIME,
+    claimed_by_user_id INTEGER,
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (claimed_by_user_id) REFERENCES users(id),
+    UNIQUE(transaction_id),
+    UNIQUE(token_hash)
+);
+
+CREATE INDEX IF NOT EXISTS idx_tokens_hash ON claim_tokens(token_hash);
+CREATE INDEX IF NOT EXISTS idx_tokens_expires ON claim_tokens(expires_at);
+
+-- 4. 마일리지 원장 테이블
+CREATE TABLE IF NOT EXISTS mileage_ledger (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id INTEGER NOT NULL,
+    transaction_id VARCHAR(20),
+    points INTEGER NOT NULL,
+    balance_after INTEGER NOT NULL,
+    reason VARCHAR(50) NOT NULL,
+    description TEXT,
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (user_id) REFERENCES users(id),
+    UNIQUE(transaction_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_ledger_user ON mileage_ledger(user_id);
+CREATE INDEX IF NOT EXISTS idx_ledger_transaction ON mileage_ledger(transaction_id);
+
+-- 5. POS 고객 연결 테이블
+CREATE TABLE IF NOT EXISTS pos_customer_links (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    user_id INTEGER NOT NULL,
+    pharmacy_id VARCHAR(20),
+    cuscode VARCHAR(10),
+    customer_name VARCHAR(50),
+    linked_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+    is_active BOOLEAN DEFAULT TRUE,
+    FOREIGN KEY (user_id) REFERENCES users(id),
+    UNIQUE(user_id, pharmacy_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_links_cuscode ON pos_customer_links(cuscode);