feat: PostgreSQL kuyruk sistemi (SSE yerine queue+poll)

Ne yaptik:
- ReportQueue modeli + Alembic migration (report_queue tablosu)
- QueueWorker: SELECT FOR UPDATE SKIP LOCKED ile tek worker polling
- 3 yeni endpoint: POST /api/queue/submit, GET /api/queue/{id}/status, GET /api/queue/active
- Startup hook ile worker otomatik basliyor, shutdown'da duruyor
- Stuck task recovery: 15 dk'dan eski PROCESSING tasklar PENDING'e donuyor

Neden yaptik:
- Esanli SSE rapor isteklerinde IP ban riski ve veri kaybi vardi
- Tek worker ile sirayla isleniyor, rate limit korunuyor
- Sifir yeni dependency: sadece PostgreSQL + mevcut scraper'lar

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/database.py

@@ -1,7 +1,7 @@
 """
 Database setup and models - PostgreSQL
 """
-from sqlalchemy import create_engine, Column, Integer, String, DateTime, Boolean, ForeignKey
+from sqlalchemy import create_engine, Column, Integer, String, DateTime, Boolean, ForeignKey, Text
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import sessionmaker, relationship
 from datetime import datetime
@@ -12,8 +12,7 @@ log = get_logger("db")
 
 # PostgreSQL database - configurable via environment variable
 # Default: Local PostgreSQL for development
-# Docker: postgresql://postgres:trendyol123@postgres:5432/trendyol_db
-DATABASE_URL = os.getenv("DATABASE_URL", "postgresql://postgres:trendyol123@localhost:5433/trendyol_db")
+DATABASE_URL = os.getenv("DATABASE_URL", "postgresql://postgres@localhost:5433/trendyol_db")
 
 engine = create_engine(DATABASE_URL, pool_pre_ping=True)
 SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
@@ -84,6 +83,25 @@ class EnrichmentError(Base):
     created_at = Column(DateTime, default=datetime.utcnow)
 
 
+class ReportQueue(Base):
+    """Queue for report generation tasks"""
+    __tablename__ = "report_queue"
+
+    id = Column(Integer, primary_key=True, index=True)
+    report_name = Column(String, nullable=False)
+    category_id = Column(Integer, nullable=False)
+    status = Column(String, nullable=False, default="PENDING")
+    progress = Column(Integer, nullable=False, default=0)
+    message = Column(Text, nullable=True)
+    result_report_id = Column(Integer, nullable=True)
+    error = Column(Text, nullable=True)
+    worker_id = Column(String, nullable=True)
+    created_at = Column(DateTime, default=datetime.utcnow)
+    started_at = Column(DateTime, nullable=True)
+    completed_at = Column(DateTime, nullable=True)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+
+
 def init_db():
     """Initialize database - create tables"""
     Base.metadata.create_all(bind=engine)