feat(models): Phase 1 SQLAlchemy models — SessionFact, SessionSuggestedFix, DraftTemplate, AccountSettings

Backs the schema added in 210d310 with SQLAlchemy 2.0 models.

- SessionFact: "What we know" facts with polymorphic source_ref pointing
  at task-lane item UUIDs inside ai_sessions.pending_task_lane (not a FK
  per Section 4.2).
- SessionSuggestedFix: AI-proposed resolutions with supersession tracking
  and the full user_decision state machine.
- DraftTemplate: post-resolve templatization queue with promotion to
  script_templates.
- AccountSettings: per-account JSONB preferences grab-bag with async
  classmethod helpers — get_setting(db, account_id, key, default) reads
  without creating, set_setting(db, account_id, key, value) upserts via
  Postgres ON CONFLICT + jsonb `||` merge so existing keys are preserved.
  Lazy row creation matches the Phase 1 design.

Column additions on existing models to mirror the migration:
- AISession: resolution_note_* / escalation_package_* / state_version
  (the preview-cache-invalidation counter consumed by Phase 3).
- ScriptTemplate: source_session_id / source_user_id / source_ticket_ref
  (provenance for templates promoted from DraftTemplate).

All four new models registered in app.models.__init__ and __all__.
TYPE_CHECKING-guarded relationship imports throughout, matching the
repo's existing model style.

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

backend/app/models/draft_template.py

@@ -0,0 +1,91 @@
+"""Draft template model — scripts generated during a session, pending templatization.
+
+Created when an engineer picks "Run now, templatize after resolve" in the
+three-option dialog. Post-resolve, the TemplatizePrompt component reads pending
+drafts and lets the engineer accept (promotes to `script_templates`) or reject.
+"""
+import uuid
+from datetime import datetime, timezone
+from typing import Any, TYPE_CHECKING
+
+from sqlalchemy import (
+    Text, DateTime, ForeignKey, String, CheckConstraint,
+)
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+
+from app.core.database import Base
+
+if TYPE_CHECKING:
+    from app.models.account import Account
+    from app.models.ai_session import AISession
+    from app.models.user import User
+    from app.models.script_template import ScriptCategory, ScriptTemplate
+
+
+class DraftTemplate(Base):
+    """A session-generated script pending conversion to a reusable template."""
+    __tablename__ = "draft_templates"
+    __table_args__ = (
+        CheckConstraint(
+            "status IN ('pending', 'accepted', 'rejected')",
+            name="ck_draft_templates_status",
+        ),
+    )
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+    )
+    account_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("accounts.id"),
+        nullable=False,
+    )
+    source_session_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("ai_sessions.id"),
+        nullable=False,
+    )
+    source_user_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("users.id"),
+        nullable=False,
+    )
+    script_body: Mapped[str] = mapped_column(Text, nullable=False)
+    proposed_parameters: Mapped[dict[str, Any]] = mapped_column(
+        JSONB, nullable=False
+    )
+    proposed_name: Mapped[str | None] = mapped_column(String(200), nullable=True)
+    proposed_category_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("script_categories.id"),
+        nullable=True,
+    )
+    status: Mapped[str] = mapped_column(
+        String(32), nullable=False, default="pending"
+    )
+    resolved_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    # Set when status transitions to 'accepted' and the draft is promoted
+    # to a real script_templates row.
+    promoted_template_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True),
+        ForeignKey("script_templates.id"),
+        nullable=True,
+    )
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
+    )
+
+    account: Mapped["Account"] = relationship("Account", foreign_keys=[account_id])
+    source_session: Mapped["AISession"] = relationship(
+        "AISession", foreign_keys=[source_session_id]
+    )
+    source_user: Mapped["User"] = relationship("User", foreign_keys=[source_user_id])
+    proposed_category: Mapped["ScriptCategory | None"] = relationship(
+        "ScriptCategory", foreign_keys=[proposed_category_id]
+    )
+    promoted_template: Mapped["ScriptTemplate | None"] = relationship(
+        "ScriptTemplate", foreign_keys=[promoted_template_id]
+    )