feat: Phase 1 Group 7 — add account_id to script tables (keep team_id)

team_id is kept in all three tables — drop deferred until app code
is fully migrated off team_id references.

Tables: script_builder_sessions, script_templates, script_generations
Backfill: user_id/created_by → users.account_id

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

backend/app/models/script_template.py

@@ -44,6 +44,12 @@ class ScriptTemplate(Base):
     team_id: Mapped[Optional[uuid.UUID]] = mapped_column(
         UUID(as_uuid=True), ForeignKey("teams.id", ondelete="CASCADE"), nullable=True, index=True
     )
+    account_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("accounts.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
     created_by: Mapped[Optional[uuid.UUID]] = mapped_column(
         UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=True
     )
@@ -97,6 +103,12 @@ class ScriptGeneration(Base):
     user_id: Mapped[uuid.UUID] = mapped_column(
         UUID(as_uuid=True), ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
     )
+    account_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("accounts.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
     team_id: Mapped[Optional[uuid.UUID]] = mapped_column(
         UUID(as_uuid=True), ForeignKey("teams.id", ondelete="SET NULL"), nullable=True, index=True
     )