feat: enrich daily bar schema with valuation/status fields + VWAP

Batch download now pulls baostock's preclose, turn, pctChg, tradestatus,
isST, and peTTM/pbMRQ/psTTM/pcfNcfTTM on top of OHLCV+amount, plus a
derived daily VWAP (amount/volume). VWAP is raw-price scale and not
comparable with adjusted OHLC under qfq/hfq — documented in the schema.

Richer fields live only in the batch path (download_daily_batch ->
download_universe); single-symbol download_daily keeps the legacy
8-column schema that test_downloader.py pins. Also flags intraday/L1-L2
microstructure data as a future phase in the README roadmap.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CLAUDE.md

@@ -42,7 +42,7 @@ An **alpha** is a signed cross-sectional **position weight**: positive = long, n
 ## Parquet schema contracts
 
 `pipeline/common/schema.py` defines the column contracts that are the *only* interface between phases. Any new phase or alpha must conform:
-- `DATA_COLUMNS` (data output): `symbol_id, symbol_name, date, open, high, low, close, volume, amount`
+- `DATA_COLUMNS` (data output): `symbol_id, symbol_name, date, open, high, low, close, preclose, volume, amount, vwap, turn, pctChg, tradestatus, isST, peTTM, pbMRQ, psTTM, pcfNcfTTM` (`vwap` = `amount/volume` is a raw-price daily VWAP, *not* on the adjusted OHLC scale under qfq/hfq). The richer fields are fetched only by the **batch** path (`download_daily_batch` → `download_universe`); single-symbol `download_daily` keeps the legacy 8-column schema that `tests/test_downloader.py` pins.
 - `ALPHA_COLUMNS` (alpha output): `symbol_id, date, alpha_name, weight`
 - `COMBO_COLUMNS` (combo output): `symbol_id, date, combo_name, weight`