feat: add certificate management module with image upload

- Add Certificate + CertificateCategory models with full CRUD API
- Image upload via base64 data URL stored in Text column
- Certificate fields: title, issuer, issue_date, expiry_date, image, description
- Frontend: card grid with category sidebar filter, create/edit dialog
- Include certificates in data backup/export
- Fix hasPhaseParent optimization in GoalDetailPage

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/app/models/certificate.py

@@ -0,0 +1,43 @@
+import uuid as _uuid
+from sqlalchemy import Column, Integer, String, Text, Date, Boolean, DateTime, ForeignKey
+from sqlalchemy.orm import relationship
+from app.database import Base
+from app.utils.datetime import utcnow
+
+
+class CertificateCategory(Base):
+    """证书分类模型"""
+    __tablename__ = "certificate_categories"
+
+    id = Column(Integer, primary_key=True, index=True)
+    uuid = Column(String(36), default=lambda: str(_uuid.uuid4()), unique=True, index=True)
+    name = Column(String(50), nullable=False)
+    icon = Column(String(50), default="medal")
+    color = Column(String(20), default="#FFB7C5")
+    sort_order = Column(Integer, default=0)
+    is_deleted = Column(Boolean, default=False)
+    sync_version = Column(Integer, default=1)
+
+    certificates = relationship("Certificate", back_populates="category")
+
+
+class Certificate(Base):
+    """证书模型"""
+    __tablename__ = "certificates"
+
+    id = Column(Integer, primary_key=True, index=True)
+    uuid = Column(String(36), default=lambda: str(_uuid.uuid4()), unique=True, index=True)
+    title = Column(String(200), nullable=False)
+    category_id = Column(Integer, ForeignKey("certificate_categories.id"), nullable=True)
+    image = Column(Text, nullable=True)  # base64 data URL
+    issuer = Column(String(200), nullable=True)  # 来源/颁发机构
+    issue_date = Column(Date, nullable=True)
+    expiry_date = Column(Date, nullable=True)  # null = 永久有效
+    description = Column(Text, nullable=True)
+    sort_order = Column(Integer, default=0)
+    is_deleted = Column(Boolean, default=False)
+    sync_version = Column(Integer, default=1)
+    created_at = Column(DateTime, default=utcnow)
+    updated_at = Column(DateTime, default=utcnow, onupdate=utcnow)
+
+    category = relationship("CertificateCategory", back_populates="certificates")