feat(admissions): publish the latest cut-off only, holding history back

Earlier years are to become a paid feature, so they stop being published.

The load-bearing part is that this is a change to the API, not only to the
page. /api/schools/{urn} is public and unauthenticated: leaving
admission_distance_history in the payload while declining to render it would
have handed the whole record to anyone who opened the network tab. It is
withheld at the source, and the page follows.

Nothing changes upstream. The tap, the plausibility band and
fact_admission_distance are untouched and still load every published year, so
restoring history for entitled callers is a change to one function in
data_loader rather than a re-collection.

What the reader now gets is the latest figure on the Admissions tile, and a
Distance section that answers the question the number alone cannot: whether
their own address falls inside it. Retitled to "How far away are you?", which
is what it now does — the previous title described a record that is no longer
there.

Removed with the history: the trend chart, the year-by-year table, the
per-year verdict strip, the trend summary and the coverage note, along with
their CSS. The section goes from 743px to 417px.

One consequence worth naming. A run of years used to soften a single close
call — a home just outside one year's cut-off was usually inside another. With
one year published, the "too close to call" band is the entire safety margin
between a parent and a place they do not have, so the verdict now names its
year, and the three outcomes are tinted apart rather than distinguished by
wording alone.

The existing stylesheet test earned its keep here: the three verdict classes
were referenced before they were written, and it caught them. Unstyled, a
"beyond the cut-off" result would have been indistinguishable from an "inside"
one — the exact failure the longhand class map was written to prevent.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WDvkyqqHABm4bmth2kjAxE

backend/tests/test_supplementary_batch.py

@@ -151,11 +151,13 @@ def test_one_query_per_table_and_latest_row_per_urn():
     assert out[1]["admissions"]["year"] == 202627
     assert out[2]["admissions_history"] == [{**out[2]["admissions_history"][0]}]
 
-    # Cut-off distance: full history oldest-first, with the newest year also
-    # exposed on its own. The fixture rows are deliberately out of order, so
-    # this only passes if the query's ORDER BY is doing the work.
-    assert [r["year"] for r in out[1]["admission_distance_history"]] == [2024, 2025, 2026]
+    # Cut-off distance: the latest year only. Earlier years stay in the mart
+    # but are held back as a paid feature, and this API is public — serving
+    # them here would hand them to anyone reading the response. The fixture
+    # rows are deliberately out of order, so "latest" only comes out right if
+    # the query's ORDER BY is doing the work.
     assert out[1]["admission_distance"]["year"] == 2026
+    assert "admission_distance_history" not in out[1]
     assert out[1]["admission_distance"]["distance_m"] == 529.47
     # route_count travels with the figure — the page needs it to say the
     # distance is the furthest of several bands rather than the only one.
@@ -171,4 +173,4 @@ def test_single_wrapper_matches_batch(monkeypatch):
     assert single["ofsted"]["overall_effectiveness"] == 2
     assert single["admissions_history"] == []
     assert single["admission_distance"] is None
-    assert single["admission_distance_history"] == []
+    assert "admission_distance_history" not in single