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/script_template.py

@@ -78,6 +78,20 @@ class ScriptTemplate(Base):
     is_gallery_featured: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False, server_default=text("false"), index=True)
     gallery_sort_order: Mapped[int] = mapped_column(Integer, nullable=False, default=0, server_default=text("0"))
     usage_count: Mapped[int] = mapped_column(Integer, nullable=False, default=0, server_default=text("0"))
+    # ── Provenance (Phase 1 — FlowPilot migration) ──
+    # Populated when a template is promoted from a post-resolve draft_templates row.
+    # Powers the Script Library provenance chip:
+    # "generated from CW #X · resolved by Y · used N times"
+    source_session_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("ai_sessions.id"), nullable=True,
+    )
+    source_user_id: Mapped[Optional[uuid.UUID]] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("users.id"), nullable=True,
+    )
+    source_ticket_ref: Mapped[Optional[str]] = mapped_column(
+        String(64), nullable=True,
+        comment="Human-readable PSA ticket ref for display, e.g. 'CW #48307'",
+    )
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
     )