Label the funders histogram axes, and quiet the clean checks on /relation_integrity

[robsv]

Two unrelated UI fixes, three commits.

/funders — the histogram had no axis labels

dis_plots has no single-series vertical bar chart. The only bar options are
stacked_bar_chart and hbar_chart, which is horizontal — so the histogram
was drawn by stacking a single series. That renders correctly (vbar_stack of
one series is a plain vbar), but it left the chart with nothing naming its
axes.

The cause is that stacked_bar_chart identifies its series through a legend,
so it never sets an axis label. Of its thirteen callers the funders histogram
is the only one passing legend=False, and the only single-series one:
having suppressed the legend it had no label of any kind left. The other twelve
are genuinely stacked, read fine from their legends, and are untouched.

Adds bar_chart — the vertical counterpart to hbar_chart — taking x_label
and y_label that default to the field names. Same color, grid, baseline and
background as before, so the only visual change is the labels, and it carries
the same _make_clickable drill-down support as its neighbours. No legend to
suppress.

The histogram now reads Funders named on a record against Records.

/relation_integrity — clean checks were shouting

Eight checks run; four are clean on current data. Each clean one rendered a
heading, a paragraph explaining the check, and "Nothing found." — and got a
summary card at the top reading 0, linking down to that "Nothing found."
Half the page, and half the card row, was about things that had not happened.

Two changes, both only affecting checks with no findings:

• The explanatory paragraph goes. It explains what to do about a finding,
  which is moot when there are none. The heading stays: it is what makes the
  severity-band counts reconcile, and (0) is itself the useful statement —
  the check ran and found nothing.
• The card goes. The row is the at-a-glance summary of what needs
  attention. Current data takes it from eight cards to four. The (0) headings
  below still show every check that ran, so nothing is hidden.

Guarded for the all-clean case, where the card list is empty and stat_cards
would render a bare row: that reads "Every check is clean."

Nothing changes for a section that has findings.

Verification

Both pages checked against a running server.

The chart's rendered Bokeh payload carries both labels and no legend:

"axis_label":"Funders named on a record"
"axis_label":"Records"
"VBar" × 3 Legend × 0

/relation_integrity asserted per section — all 8 correct: the 4 clean ones
heading-plus-"Nothing found." with no paragraph, the 4 with findings unchanged,
and 4 cards rendered rather than 8, none reading zero.

113 tests pass. No new lint messages — the C0302 on dis_plots.py was
already present on main at 1185/1000; these 46 lines moved the number, not the
verdict.

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