refactor: class-based alpha factory + month-partitioned data pipeline

Replace the old signal/strategy/backtest modules with a decoupled
data → alpha → combo pipeline (parquet between phases, .pq extension).

Alphas:
- BaseAlpha + @register_alpha factory/plugin registry; one file per
  built-in (reversal, reversal_vol, momentum); external alphas via
  --alpha-module. Alphas are z-scored position weights, not predictors.

Data:
- baostock primary / akshare fallback, treated consistently.
- New --universe all (~5000 A-shares via query_all_stock, filtered).
- login-once batch downloader; empty-string OHLCV coerced to NaN.
- Month-partitioned dataset {output_dir}/{universe}/month=YYYY-MM/*.pq
  with chunked durability flushes; --data-path is the dataset dir.

CLI logs at INFO by default (--log-level) so progress is visible.
Docs (README, CLAUDE.md) updated incl. pipeline diagram and roadmap
TODOs for portfolio construction / backtest / paper trading.

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

cli.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python3
+"""Chinese Equity Quant Pipeline — decoupled phase CLI.
+
+Phases:
+    data    — Download daily bars to parquet
+    alpha   — Compute alpha weights from data
+    combo   — Combine alphas into a single weight
+"""
+
+import logging
+
+import click
+
+from pipeline.data.cli import data
+from pipeline.alpha.cli import alpha
+from pipeline.combo.cli import combo
+
+
+@click.group()
+@click.option(
+    "--log-level", default="INFO",
+    type=click.Choice(["DEBUG", "INFO", "WARNING", "ERROR"], case_sensitive=False),
+    help="Logging verbosity (default INFO shows download/compute progress)",
+)
+def cli(log_level):
+    """Chinese Equity Quant Pipeline.
+
+    Each phase is independent: read from parquet, write to parquet.
+    """
+    logging.basicConfig(
+        level=getattr(logging, log_level.upper()),
+        format="%(asctime)s %(levelname)s %(name)s: %(message)s",
+        datefmt="%H:%M:%S",
+    )
+
+
+cli.add_command(data)
+cli.add_command(alpha)
+cli.add_command(combo)
+
+
+if __name__ == "__main__":
+    cli()