fix(enterprise): escape pipes and newlines in Markdown Actions table (#338) - #355

Problem

In the Actions table of QualityReport.to_markdown(), only the description
cell was escaped. A column named a|b therefore added an extra cell and
shifted the whole row, and a newline in any cell split the row. This breaks the
rendered table (issue #338).

Reproduction on main:

import pandas as pd, freshdata as fd
from freshdata.enterprise import build_quality_report

df = pd.DataFrame({"a|b": [" x", "y ", "z", "w"], "k": [1, 2, 3, 4]})
out, rep = fd.clean(df, return_report=True, verbose=False, column_names=False)
print(build_quality_report(df, out, rep).to_markdown())
# Actions data row has 5 cells while the header has 4.

Fix

• Escape every cell inside _md_table_row via a small _md_escape_cell
  helper: | becomes \|, and \r\n / \r / \n become <br>.
• Remove the now-redundant a.description.replace("|", "\|") at the call site
  so values are no longer double-escaped.

The separator/header rows contain no pipes or newlines, so their rendering is
unchanged.

Tests

• test_md_table_row_escapes_pipe_and_newline — unit-covers pipe escaping and
  bare-\r, CRLF and \n line breaks.
• test_quality_report_actions_table_survives_pipe_in_column_name — regression
  for QualityReport.to_markdown breaks the Actions table when a column name contains '|' #338: every Actions row keeps the header's column count and shows a\|b.

Verification (run locally)

• pytest -m "not online and not large" — coverage gate reached (93.21%); the
  only failures are 3 pre-existing, unrelated tests (performance/test_runner_cli,
  test_experimental_ai_copilot, test_semantic_backends) that also fail on an
  unmodified main in this environment.
• pytest tests/test_enterprise_metrics.py --no-cov — all pass.
• ruff check . — clean.

I also added a note under Unreleased → Fixed in CHANGELOG.md.