feat: add pqcat helper to inspect parquet files

A standalone tools/pqcat.py (head/tail/columns/info) wired as `cli.py pqcat`
and runnable directly via a PATH symlink, plus README docs.

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

tools/__init__.py

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+"""Standalone helper tools (not part of the data→alpha→combo pipeline)."""

tools/pqcat.py

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+#!/usr/bin/env python3
+"""CLI helper to inspect parquet files, like `cat` for `.pq`."""
+
+import click
+import pandas as pd
+
+
+@click.command(name="pqcat")
+@click.argument("path", type=click.Path(exists=True))
+@click.option("-n", "--head", "head", type=int, default=None, help="Show only the first N rows")
+@click.option("-t", "--tail", "tail", type=int, default=None, help="Show only the last N rows")
+@click.option("-c", "--columns", default=None, help="Comma-separated subset of columns to show")
+@click.option("--info", is_flag=True, help="Show shape + dtypes instead of the rows")
+def pqcat(path, head, tail, columns, info):
+    """Dump a parquet file (or partitioned dataset dir) to stdout.
+
+    PATH is a single .pq file or a Hive-partitioned dataset directory.
+    """
+    df = pd.read_parquet(path)
+
+    if columns:
+        cols = [c.strip() for c in columns.split(",") if c.strip()]
+        missing = [c for c in cols if c not in df.columns]
+        if missing:
+            raise click.ClickException(f"Columns not found: {', '.join(missing)}")
+        df = df[cols]
+
+    if info:
+        click.echo(f"path:    {path}")
+        click.echo(f"shape:   {df.shape[0]:,} rows x {df.shape[1]} cols")
+        click.echo("dtypes:")
+        for name in df.columns:
+            click.echo(f"  {name}: {df[name].dtype}")
+        return
+
+    if head is not None:
+        df = df.head(head)
+    elif tail is not None:
+        df = df.tail(tail)
+
+    with pd.option_context(
+        "display.max_rows", None if (head is None and tail is None) else len(df),
+        "display.max_columns", None,
+        "display.width", None,
+    ):
+        click.echo(df.to_string(index=False))
+
+
+if __name__ == "__main__":
+    pqcat()