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>

pipeline/combo/cli.py

@@ -0,0 +1,47 @@
+"""CLI for alpha combination."""
+
+import os
+import click
+
+from pipeline.combo.combine import combine_alphas, COMBO_METHODS
+
+
+@click.group(name="combo")
+def combo():
+    """Combine multiple alphas into a single combined weight."""
+
+
+@combo.command("combine")
+@click.option(
+    "--alpha-paths", required=True,
+    help="Comma-separated paths to alpha parquet files",
+)
+@click.option("--combo-name", required=True, help="Name for this combo")
+@click.option(
+    "--method", default="equal_weight",
+    type=click.Choice(list(COMBO_METHODS.keys())),
+    help="Combination method",
+)
+@click.option("--output-dir", default="combos", help="Directory to save combo parquet")
+def combine(alpha_paths, combo_name, method, output_dir):
+    """Combine multiple alphas and save as parquet."""
+    paths = [p.strip() for p in alpha_paths.split(",") if p.strip()]
+    if len(paths) < 2:
+        click.echo("Error: --alpha-paths requires at least 2 comma-separated paths", err=True)
+        return
+
+    result = combine_alphas(
+        alpha_paths=paths,
+        combo_name=combo_name,
+        method=method,
+    )
+
+    os.makedirs(output_dir, exist_ok=True)
+    out_path = f"{output_dir}/{combo_name}.pq"
+    result.to_parquet(out_path, index=False)
+    click.echo(f"Saved combo: {out_path}  ({len(result):,} rows)")
+    click.echo(
+        f"Weight stats — min: {result['weight'].min():.4f}, "
+        f"max: {result['weight'].max():.4f}, "
+        f"mean: {result['weight'].mean():.4f}"
+    )