feat(rag): lite-generated KB overview in the system prompt — stored single row, regenerated on import, <knowledge_base> section in HIGH+LOW prompts

app/models.py

@@ -10,6 +10,9 @@ Data model — see ``.agent/PLAN.md`` §Data Model:
                       the deflection decision, and latency.
 * ``steering_notes`` — owner tuning notes injected into the system prompt
                       of every chat turn (phase 15, ``<tuning>`` section).
+* ``kb_overview``    — single-row lite-generated outline of the KB's basic
+                      categories, injected as the ``<knowledge_base>``
+                      section of every chat turn (phase 31).
 """
 from __future__ import annotations
 
@@ -109,3 +112,24 @@ class SteeringNote(Base):
     id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
     note: Mapped[str] = mapped_column(Text)  # trimmed, 1–2000 chars (API-enforced)
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+
+
+class KbOverview(Base):
+    """Single-row, lite-generated outline of the knowledge base (phase 31).
+
+    Exactly one row (``id = 1``, enforced by the migration 0005 server
+    defaults) holds a plain-text outline of the KB's basic categories,
+    generated by the aipi ``lite`` model whenever an import changes the KB.
+    Chat turns only read this row (one indexed PK lookup) and inject it into
+    the system prompt of every turn as the ``<knowledge_base>`` section — an
+    empty row means the section is absent and the prompt stays
+    byte-identical to the pre-phase text (phase 15 convention).
+    """
+
+    __tablename__ = "kb_overview"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, server_default="1")
+    content: Mapped[str] = mapped_column(Text, server_default="")  # the outline text
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now()
+    )