feat: brain/index.go shebang; mail import is not a brain write (D14). (#12)

Commands live at bin/brain/{index,get,stats,eval,watch}.go and
bin/mail/import.go, bin/markdown/import.go, bin/postgres/query.go.
Python remains the Ladybug write worker. index_mail is a deprecation
shim that rebuilds via --with-mail.

bin/tools/test_mailleafs.py

@@ -0,0 +1,46 @@
+"""Mail markdown → leafs (no Ladybug). Brain index --with-mail uses this."""
+from __future__ import annotations
+
+import json
+import sys
+import tempfile
+import unittest
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent))
+
+import mailleafs  # noqa: E402
+
+
+class MailLeafsTest(unittest.TestCase):
+    def test_message_md_becomes_info_leaf(self) -> None:
+        root = Path(tempfile.mkdtemp())
+        msg = root / "inbox" / "alice-1"
+        msg.mkdir(parents=True)
+        (msg / "message.json").write_text(
+            json.dumps({"receivedDate": "2026-01-15T10:00:00Z", "subject": "Hello"}),
+            encoding="utf-8",
+        )
+        (msg / "message.md").write_text(
+            "---\nroot: info\n---\n\n# Hello\n\nFrom Alice to Bob.\n",
+            encoding="utf-8",
+        )
+        leafs = mailleafs.from_mail_root(root)
+        self.assertEqual(len(leafs), 1)
+        self.assertIn("Alice", leafs[0]["text"])
+        self.assertTrue(leafs[0]["source"].startswith("ooMail:"))
+        self.assertEqual(leafs[0]["how"], "mail/import")
+
+    def test_since_filters_by_message_json_date(self) -> None:
+        root = Path(tempfile.mkdtemp())
+        for name, day in (("old", "2025-01-01"), ("new", "2026-06-01")):
+            d = root / "inbox" / name
+            d.mkdir(parents=True)
+            (d / "message.json").write_text(
+                json.dumps({"receivedDate": f"{day}T00:00:00Z"}),
+                encoding="utf-8",
+            )
+            (d / "message.md").write_text(f"# {name}\n\nbody\n", encoding="utf-8")
+        leafs = mailleafs.from_mail_root(root, since="2026-01-01")
+        self.assertEqual(len(leafs), 1)
+        self.assertIn("new", leafs[0]["text"])