fix(search): avoid year-0 crashes in Chinese rolling-window temporal extraction

[r266-tech]

Fixes #2533.

Summary

• avoid constructing year 0 when Chinese rolling-window expressions shift a low reference year backward
• return the existing no-temporal-constraint sentinel for impossible relative year shifts
• keep valid low-year rolling windows and unrelated parser ValueErrors covered by regression tests

Tests

• uv run --frozen pytest tests/test_query_analyzer.py -q
• uv run --frozen ruff format --check hindsight_api/engine/chinese_temporal_periods.py tests/test_query_analyzer.py
• uv run --frozen ruff check hindsight_api/engine/chinese_temporal_periods.py tests/test_query_analyzer.py
• python3 -m py_compile hindsight_api/engine/chinese_temporal_periods.py
• git diff --check