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>

README.md

@@ -224,7 +224,11 @@ supplies it and the unrelated `--lookback`/`--vol-window` defaults are ignored.
 The column contracts in `pipeline/common/schema.py` are the only interface
 between phases (data is stored long/tidy):
 
-- **data** (`DATA_COLUMNS`): `symbol_id, symbol_name, date, open, high, low, close, volume, amount`
+- **data** (`DATA_COLUMNS`): `symbol_id, symbol_name, date, open, high, low, close, preclose, volume, amount, vwap, turn, pctChg, tradestatus, isST, peTTM, pbMRQ, psTTM, pcfNcfTTM`
+  (`vwap` = `amount / volume` — a **raw**-price daily VWAP, *not* on the adjusted
+  OHLC scale under `qfq`/`hfq`; `turn` is turnover %, `pctChg` daily % change,
+  `tradestatus`/`isST` are 0/1 flags, and `peTTM`/`pbMRQ`/`psTTM`/`pcfNcfTTM` are
+  baostock valuation ratios.)
 - **alpha** (`ALPHA_COLUMNS`): `symbol_id, date, alpha_name, weight`
 - **combo** (`COMBO_COLUMNS`): `symbol_id, date, combo_name, weight`
 
@@ -258,6 +262,10 @@ execution modeling. The following phases are planned but not built yet:
   richer P&L / risk attribution than `alpha eval`.
 - [ ] **Forward / paper trading** — run the same construction logic on live
   daily data, track simulated fills and a running P&L without real capital.
+- [ ] **Intraday / microstructure data** — bid/ask prices & sizes, mid-price,
+  and intraday VWAP. These need a tick / L1–L2 quote feed (typically a paid or
+  brokerage data tier); the free daily sources here only expose daily bars, so
+  this is a separate data phase rather than extra columns on the daily schema.
 
 Until these land, treat `alpha eval` as a fast sanity check on a weight series,
 not a performance estimate.