feat: citations, eval sidecar/pvalue/trace, nomic prefixes

mcp 2.x already on main. Does not replace the variety chunker
(one chunk per variety is the anti-hallucination contract).

- Numbered [1] citations on search_docs / search_trials
- Eval JSONL sidecar, k-curve, eval.pvalue, eval.trace
- Nomic prefixes at embed time only; stored text unprefixed

Closes #25

eval/test_pvalue.py

@@ -0,0 +1,25 @@
+"""Stdlib tests for the permutation test. No Chroma."""
+from __future__ import annotations
+
+import unittest
+
+from eval.pvalue import paired_permutation
+
+
+class PermutationTests(unittest.TestCase):
+    def test_identical_is_not_significant(self) -> None:
+        a = [1.0, 0.5, 0.0, 1.0]
+        r = paired_permutation(a, list(a), n_resamples=200, seed=0)
+        self.assertEqual(r["Diff(A-B)"], 0.0)
+        self.assertFalse(r["significant"])
+
+    def test_large_shift_is_significant(self) -> None:
+        a = [1.0] * 20
+        b = [0.0] * 20
+        r = paired_permutation(a, b, n_resamples=500, seed=0)
+        self.assertTrue(r["significant"])
+        self.assertLess(r["p_value"], 0.05)
+
+
+if __name__ == "__main__":
+    unittest.main()