db: add digest opt-in/tone on users, email_sends audit table

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/models.py

@@ -22,6 +22,7 @@ from sqlalchemy import (
     String,
     Text,
     UniqueConstraint,
+    text,
 )
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
@@ -174,6 +175,12 @@ class User(Base):
     credit_until: Mapped[datetime | None] = mapped_column(
         DateTime(timezone=True), nullable=True,
     )
+    email_digest_opt_in: Mapped[bool] = mapped_column(
+        Boolean, nullable=False, default=True, server_default=text("1"),
+    )
+    # NULL = use INTERMEDIATE at render time. Server-side mirror of the
+    # dashboard tone, decoupled because the dashboard pref is localStorage.
+    digest_tone: Mapped[str | None] = mapped_column(String(16))
 
     __table_args__ = (
         UniqueConstraint("email", name="uq_users_email"),
@@ -311,3 +318,25 @@ class JobRun(Base):
     items_written: Mapped[int | None] = mapped_column(Integer)
 
     __table_args__ = (Index("ix_jobruns_name_started", "name", "started_at"),)
+
+
+class EmailSend(Base):
+    """Audit row per digest email send. Used for idempotency (don't send
+    twice on the same UTC day) and for surfacing 'last delivery' on the
+    Settings page."""
+    __tablename__ = "email_sends"
+
+    id: Mapped[int] = mapped_column(BigInteger, primary_key=True, autoincrement=True)
+    user_id: Mapped[int] = mapped_column(
+        ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True,
+    )
+    kind: Mapped[str] = mapped_column(String(16), nullable=False)   # "daily" | "weekly"
+    sent_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=utcnow, nullable=False,
+    )
+    status: Mapped[str] = mapped_column(String(16), nullable=False) # "sent" | "skipped" | "error"
+    error: Mapped[str | None] = mapped_column(String(255))
+
+    __table_args__ = (
+        Index("ix_email_sends_user_kind_sent", "user_id", "kind", "sent_at"),
+    )