feat: port template upgrades (citations, eval, chunking, nomic prefixes)

mcp 2.x is already on origin/main. This ports the rest of
docs-mcp-template #12–#16 without replacing HVM's BM25-first
search_docs path.

- Numbered [1] citations via docs_mcp/format.py
- Eval P@1 + JSONL sidecar + eval.pvalue
- Heading-recursive chunker, keep chunk-0 and MAX_CHARS=4000
- Nomic prefixes at embed time only; stored text unprefixed

Closes #15

docs_mcp/test_format.py

@@ -0,0 +1,37 @@
+"""Citation markdown renderer — no Chroma, no mcp."""
+from __future__ import annotations
+
+import unittest
+
+from docs_mcp.format import format_search_hits
+
+
+class FormatSearchHitsTests(unittest.TestCase):
+    def test_two_hits_numbered_with_urls(self) -> None:
+        out = format_search_hits([
+            ("Install on Linux", "https://docs.example.com/install", "chunk one", ""),
+            ("HA setup", "https://docs.example.com/ha", "chunk two", ""),
+        ])
+        self.assertIn("[1] **Install on Linux** — https://docs.example.com/install", out)
+        self.assertIn("[2] **HA setup** — https://docs.example.com/ha", out)
+        self.assertIn("chunk one", out)
+        self.assertIn("chunk two", out)
+        self.assertNotIn("[3]", out)
+        # [1] before [2]
+        self.assertLess(out.index("[1]"), out.index("[2]"))
+        # each number is followed by its URL on the same logical hit
+        first = out.split("[2]")[0]
+        self.assertIn("https://docs.example.com/install", first)
+        self.assertNotIn("https://docs.example.com/ha", first)
+
+    def test_empty_hits_invents_nothing(self) -> None:
+        self.assertEqual(format_search_hits([]), "")
+
+    def test_missing_url_omits_emdash(self) -> None:
+        out = format_search_hits([("Title only", "", "body", "")])
+        self.assertIn("[1] **Title only**", out)
+        self.assertNotIn("—", out)
+
+
+if __name__ == "__main__":
+    unittest.main()