feat: track imported accounts per upstream key across platforms

Add upstream_key_account_links table mapping generated keys to remote
accounts per website/platform, surface imported_accounts on key
responses, and update website sync/routers to manage the links.

backend/app/models/upstream_key.py

@@ -2,7 +2,7 @@ from datetime import datetime, timezone
 from typing import Optional
 
 from sqlalchemy import DateTime, ForeignKey, Index, Integer, String, Text, UniqueConstraint
-from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.database import Base
 
@@ -30,7 +30,30 @@ class UpstreamGeneratedKey(Base):
     created_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc))
     updated_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))
 
+    account_links = relationship("UpstreamKeyAccountLink", back_populates="upstream_key", cascade="all, delete-orphan")
+
     __table_args__ = (
         UniqueConstraint("upstream_id", "group_id", "key_name", name="uq_upstream_group_key"),
         Index("ix_key_upstream_name", "upstream_id", "key_name"),
     )
+
+
+class UpstreamKeyAccountLink(Base):
+    __tablename__ = "upstream_key_account_links"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, index=True)
+    upstream_key_id: Mapped[int] = mapped_column(Integer, ForeignKey("upstream_generated_keys.id", ondelete="CASCADE"), index=True, nullable=False)
+    website_id: Mapped[int] = mapped_column(Integer, ForeignKey("websites.id", ondelete="CASCADE"), index=True, nullable=False)
+    target_group: Mapped[str] = mapped_column(String(255), nullable=False)
+    platform: Mapped[str] = mapped_column(String(64), nullable=False)
+    remote_account_id: Mapped[str] = mapped_column(String(255), nullable=False)
+    status: Mapped[str] = mapped_column(String(32), default="active", nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc))
+    updated_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))
+
+    upstream_key = relationship("UpstreamGeneratedKey", back_populates="account_links")
+
+    __table_args__ = (
+        UniqueConstraint("upstream_key_id", "website_id", "platform", name="uq_key_website_platform"),
+        UniqueConstraint("website_id", "remote_account_id", name="uq_website_remote_account"),
+    )

backend/app/models/website.py

@@ -42,6 +42,7 @@ class WebsiteGroupBinding(Base):
     percent: Mapped[str] = mapped_column(String(32), default="0")
     algorithm: Mapped[str] = mapped_column(String(64), default="priority_weighted_plus_percent")
     enabled: Mapped[bool] = mapped_column(Boolean, default=True)
+    platform: Mapped[Optional[str]] = mapped_column(String(64), nullable=True)
     created_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc))
     updated_at: Mapped[datetime] = mapped_column(
         DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc)