Extend free-text search (q) to also match payload

Cross-shard search already worked transparently across all monthly
JSON files. This adds payload content (e.g. commit SHA, meeting
attendees, structured data) to the q= substring match, alongside
title and body.

tests/test_storage.py

@@ -119,6 +119,18 @@ def test_search_free_text_matches_title_and_body(store):
     assert len(results) == 2
 
 
+def test_search_free_text_matches_payload(store):
+    store.create(_mk(title="commit", payload={"sha": "abc123def", "author": "Henrik Jess"}))
+    store.create(_mk(title="other commit", payload={"sha": "zzz999", "author": "Someone Else"}))
+    results = store.search(SearchQuery(q="abc123def"))
+    assert len(results) == 1
+    assert results[0].title == "commit"
+
+    results = store.search(SearchQuery(q="henrik"))
+    assert len(results) == 1
+    assert results[0].title == "commit"
+
+
 def test_search_respects_limit_and_offset_and_sort_order(store):
     for i in range(5):
         store.create(_mk(object_date=date(2026, 1, 1 + i), title=f"obj{i}"))