Sources: accepted-duplicate % (curation-quality signal)

Per Codex's optional note: alongside the ingest-wide duplicate_rate, expose
accepted_dup_rate — of what a source got ACCEPTED, how much was a duplicate of
already-served content (accepted_total − served). Nearly free (derived from
existing counts); surfaced as a tooltip on the Dup column so the table stays
uncluttered.

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

tests/test_dashboard.py

@@ -47,6 +47,8 @@ def test_source_health_orders_failing_first_and_computes_next_due(tmp_path):
     assert flaky["next_due_at"] is not None
     good = next(s for s in sh if s["name"] == "Good")
     assert good["served"] == 1 and good["next_due_at"] is None  # never attempted → due now
+    # source 1: 2 accepted (art 1, art 3) but art 3 is a duplicate → 50% of accepted were dupes
+    assert good["accepted_dup_rate"] == 50
 
 
 def test_attention_flags_resting_flagged_and_brief():