improve CSCL QA app page

[damonmcc]

related to #2315

improvements to CSCL diff generation and the QA app CSCL page

poc_validation/ scripts

• run_validation.py (new) — generates diffs by streaming dev and prod files directly from S3, no disk usage for inputs, no full build required
• validate_outputs.sh — writes validation_summary.csv with per-file prod row counts; mkdir -p so it's re-runnable; adds a note that run_validation.py is now the primary method
• summarize_diffs.py — reads validation_summary.csv to add # of rows in prod and % of rows with diffs columns to the summary CSV

QA app

• diff row viewer: select a file with diffs, see the dev-only rows streamed from S3 on demand
• field-level diffs section: reads from the existing dbt etl_dev_qa models (LION DAT, ThinLION, RPL) grouped by output type

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.99%. Comparing base (45fad47) to head (482d42f).

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