fix(bakery): remove income column from demographics CSV and fix dataset description

[n-issei-777]

Description

This PR fixes a critical data alignment (column shift) bug and resolves a privacy concern regarding data in the launchmybakery BigQuery setup.

1. Strip Income Column and Fix Demographics Shift

• The Issue:
  Since median_household_income remained in the source data/demographics.csv file, bq load (which maps columns positionally for CSV) actually imported the income data under the column name total_population.

  This caused:

  1. The income data to still be loaded into BigQuery.
  2. A 1-column left shift, corrupting all subsequent columns (e.g., actual populations loaded into median_age, making residents appear 33626 years old, and completely discarding foot_traffic_index).

• The Fix:
  Since the income column is not queried or utilized anywhere in the agent or tool code, I have completely removed the median_household_income column (and its header) from the source data/demographics.csv file.

2. Define Dataset Description Variable

• The Issue:
  The dataset creation command was using --description "$DATASET_DESCRIPTION", but the variable $DATASET_DESCRIPTION was never initialized, resulting in an empty dataset description.

• The Fix:
  Defined DATASET_DESCRIPTION="Dataset for MCP Bakery Demo" at the top of setup_bigquery.sh.