Setup banner, assessment timestamps, and installation docs

Instructor home shows a setup banner while a course has no class
schedule, since that is the one gap that degrades the student
experience (free-date opt-outs, no withdrawal locking); it points at
the prefilled schedule form and settings and disappears once any
class day exists.

Calls gain assessment_entered_at, stamped when an outcome is recorded
or actually changed (bulk saves that change nothing don't restamp),
null for pending calls and legacy imports, and included in the calls
export — distinguishing assessed-in-class from assessed-later.

The README setup section now gives both install routes: pure
pip/venv, and Debian system packages with the apt line. Fixing this
uncovered that numpy was missing from the project dependencies (the
grading engine needs it; the system-site-packages venv had masked
the omission).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_instructor_ui.py

@@ -5,7 +5,8 @@ import pytest
 
 from conftest import outcome_actions
 
-TODAY = datetime.date.today().isoformat()
+TODAY_DATE = datetime.date.today()
+TODAY = TODAY_DATE.isoformat()
 
 
 @pytest.fixture
@@ -95,6 +96,79 @@ def test_regenerate_replaces_pending_and_labels_change(instructor):
     assert "already have recorded outcomes" in page
 
 
+def test_assessment_entered_at_stamping(instructor):
+    from coldcall_lti.models import Call
+
+    # Live flow: pending call has no stamp; recording an outcome sets it.
+    instructor.post("/instructor/live/next", data={"date": TODAY})
+    page = instructor.get(f"/instructor/live?date={TODAY}").get_data(as_text=True)
+    call_id = int(re.search(r"/instructor/call/(\d+)/outcome", page).group(1))
+
+    app = instructor.application
+
+    def entered_at(cid):
+        with app.app_context():
+            db = app.extensions["db_session_factory"]()
+            value = db.get(Call, cid).assessment_entered_at
+            db.close()
+            return value
+
+    assert entered_at(call_id) is None
+    instructor.post(
+        f"/instructor/call/{call_id}/outcome",
+        data={"action": outcome_actions(page)["GOOD"]},
+    )
+    first_stamp = entered_at(call_id)
+    assert first_stamp is not None
+
+    # A day-editor save that changes nothing does not restamp; a real
+    # change does.
+    edit = instructor.get(f"/instructor/day/{TODAY}").get_data(as_text=True)
+    good_id = re.search(
+        r'value="(\d+)" selected>GOOD</option>', edit
+    ).group(1)
+    instructor.post(
+        f"/instructor/day/{TODAY}",
+        data={f"status-{call_id}": "answered",
+              f"assessment-{call_id}": good_id},
+    )
+    assert entered_at(call_id) == first_stamp
+
+    instructor.post(
+        f"/instructor/day/{TODAY}",
+        data={f"status-{call_id}": "missing"},
+    )
+    assert entered_at(call_id) != first_stamp
+
+    # The export carries the column.
+    csv_text = instructor.get("/instructor/export/calls.csv").get_data(as_text=True)
+    assert "assessment_entered_at" in csv_text.splitlines()[0]
+
+
+def test_setup_banner_until_schedule_exists(instructor):
+    # The dev course seeds a schedule, so no banner by default.
+    page = instructor.get("/instructor/").get_data(as_text=True)
+    assert "No class schedule yet" not in page
+
+    # Strip the schedule; the banner appears.
+    from coldcall_lti.models import ClassDay
+
+    app = instructor.application
+    with app.app_context():
+        db = app.extensions["db_session_factory"]()
+        db.query(ClassDay).delete()
+        db.commit()
+        db.close()
+    page = instructor.get("/instructor/").get_data(as_text=True)
+    assert "No class schedule yet" in page
+
+    # Adding a single class day dismisses it.
+    future = (TODAY_DATE + datetime.timedelta(days=30)).isoformat()
+    instructor.post("/instructor/schedule/add", data={"date": future})
+    page = instructor.get("/instructor/").get_data(as_text=True)
+    assert "No class schedule yet" not in page
+
+
 def test_home_working_date_override(instructor):
     tomorrow = (
         datetime.date.today() + datetime.timedelta(days=1)