test(demo): cover the demo app + sales-surface coherence

Adds a demo test suite on top of the data-value pins:

- tests/gui/test_app_demo.py (new, AppTest): every accounting persona
  renders with its dataset, the default/unknown-persona fallback resolves
  to bookkeeper, clicking Run produces the AFTER value (rows reduced to the
  validated count) with the watermarked download + Gumroad CTA, and
  switching persona via the quick-switch dropdown clears the stale result.
- tests/test_demo_pipelines.py (extended): cross-surface coherence —
  each persona key served by app_demo has a matching landing page whose
  iframe (?p=) and CTA (from=) point at it and that the hub links to;
  no retired Shopify/RevOps language remains in landing HTML; and the
  demo download still appends exactly one watermark row.

Full suite: 2584 passed, 91 skipped.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_demo_pipelines.py

@@ -69,3 +69,48 @@ def test_app_demo_references_each_demo_file():
         assert pipeline_file in src, f"{pipeline_file} not referenced in app_demo.py"
         assert (_DEMO / data_file).exists(), f"missing {data_file}"
         assert (_DEMO / pipeline_file).exists(), f"missing {pipeline_file}"
+
+
+# The accounting persona keys served by the demo app — each must line up with
+# a landing page that embeds the matching demo. (key, data-file stem)
+_PERSONA_KEYS = [
+    ("bookkeeper", "bank_reconciliation"),
+    ("ap-1099", "vendor_1099"),
+    ("ar-aging", "ar_open_invoices"),
+]
+_LANDING = _REPO / "landing"
+
+
+@pytest.mark.parametrize("key,stem", _PERSONA_KEYS)
+def test_landing_page_embeds_the_matching_demo(key, stem):
+    """Each landing page exists and its iframe + CTA point at this persona —
+    so the sales surface (landing -> demo app -> dataset) stays coherent."""
+    app_src = (_REPO / "src" / "gui" / "app_demo.py").read_text(encoding="utf-8")
+    assert f'"{key}"' in app_src, f"persona key {key!r} not served by app_demo.py"
+
+    page = _LANDING / key / "index.html"
+    assert page.exists(), f"missing landing page for {key}"
+    html = page.read_text(encoding="utf-8")
+    assert f"?p={key}" in html, f"{key} landing iframe doesn't load ?p={key}"
+    assert f"from={key}" in html, f"{key} landing CTA isn't tagged from={key}"
+
+    # The hub links to this persona's page.
+    hub = (_LANDING / "index.html").read_text(encoding="utf-8")
+    assert f'href="{key}/"' in hub, f"hub doesn't link to {key}/"
+
+
+def test_landing_surface_has_no_stale_persona_refs():
+    """No retired Shopify / RevOps persona language remains in landing HTML."""
+    for html_file in _LANDING.rglob("*.html"):
+        text = html_file.read_text(encoding="utf-8").lower()
+        for stale in ("shopify", "revops", "klaviyo", "hubspot"):
+            assert stale not in text, f"{stale!r} still in {html_file.relative_to(_REPO)}"
+
+
+def test_demo_app_builds_a_single_watermark_row():
+    """The demo download appends exactly one trailing watermark row
+    (DEMO-PLAN §6: the AFTER preview must read as production-quality)."""
+    src = (_REPO / "src" / "gui" / "app_demo.py").read_text(encoding="utf-8")
+    assert "DataTools demo — buy at" in src
+    # One trailing row concatenated onto the result frame.
+    assert "watermark_row" in src and "pd.concat([result.final_df, watermark_row]" in src