feat(sources): admin page to add and remove git sources (TODO.md L4)

app/models.py

@@ -13,6 +13,8 @@ Data model — see ``.agent/PLAN.md`` §Data Model:
 * ``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).
+* ``git_sources``    — admin-managed git source URLs the Sync button and
+                      import_docs clone/pull (phase 35).
 """
 from __future__ import annotations
 
@@ -133,3 +135,19 @@ class KbOverview(Base):
     updated_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), server_default=func.now()
     )
+
+
+class GitSource(Base):
+    """One admin-managed git source (phase 35).
+
+    The UI-maintained list of repo URLs the Sync button (phase 32) and
+    import_docs (phase 28) clone/pull. DB rows win over the
+    BOR_GIT_SOURCES env var, which is a fallback while this table is
+    empty (see app.rag.git_sources.effective_git_sources).
+    """
+
+    __tablename__ = "git_sources"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    url: Mapped[str] = mapped_column(Text, unique=True, nullable=False)
+    added_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())