perf(sessions): cache first-prompt titles, skip local-command noise in -l

Cursor/Claude session listing now scans only the head of each jsonl for a
title (aiTitle/customTitle/first user prompt), caches by (path, mtime, size),
and filters local-command protocol rows. COLUMNS=120 pinned in the table test.

tests/test_cli.py

@@ -788,7 +788,8 @@ class TestCursorListSessions:
             },
         ):
             result = runner.invoke(
-                cli, ["cursor", "--cwd", str(cwd), "--list"]
+                cli, ["cursor", "--cwd", str(cwd), "--list"],
+                env={"COLUMNS": "120"},
             )
             assert result.exit_code == 0, result.output
             assert "chat-abc123" in result.output