feat: cross-chat search FTS snippet highlighting (T111.1)

Replace the ``pov_summary`` column in ``search_all_memories``'s SELECT
with ``snippet(memories_fts, 0, '<mark>', '</mark>', '…', 32)`` so each
match in a result row is wrapped in ``<mark>`` for the search-results
UI. The original ``pov_summary`` is still returned alongside as a
non-highlighted fallback. Template renders ``r.snippet|safe`` — the only
HTML in the snippet output is the configured ``<mark>`` markers, so it
is safe to bypass Jinja's auto-escape.

tests/test_search_ux.py

@@ -136,6 +136,22 @@ def test_result_links_navigate_to_chat(client, tmp_path):
     assert 'href="/chats/chat_a"' in resp.text
 
 
+def test_search_results_include_fts_snippet_with_highlight(client, tmp_path):
+    """T111.1: FTS snippet() wraps each match in ``<mark>...</mark>`` so
+    the result row visually highlights the term that matched.
+
+    The seeded ``pov_summary`` is ``the rabbit darted across chat_a``;
+    SQLite's ``snippet()`` returns the column text with each match token
+    wrapped — searching for ``rabbit`` yields a snippet containing
+    ``<mark>rabbit</mark>``. Assertion is just that the marker appears
+    (the snippet may be truncated with an ellipsis when the indexed text
+    runs longer than the configured token window)."""
+    _seed_two_chats_with_memories(tmp_path / "test.db")
+    resp = client.get("/search?q=rabbit")
+    assert resp.status_code == 200
+    assert "<mark>rabbit</mark>" in resp.text
+
+
 def test_search_results_use_batched_lookups(client, tmp_path):
     """T106: hydration must not fan out to per-row ``get_bot``/
     ``get_chat``/``get_scene`` calls.