ingest: DIC from NCEI into calcofi_dic tables

[bbest]

Dataset

• Name: Dissolved Inorganic Carbon (DIC)
• Provider: NCEI / CalCOFI (Todd Martz)
• Source: CSV (~500KB) on Google Drive
• Coverage: 2008-2021
• Strategy: Merge DIC, alkalinity, pH measurements into existing bottle_measurement table (same Niskin bottles)

Checklist

• Data available on Google Drive
• /explore-dataset profile completed
• /generate-metadata redefinition files created
• flds_redefine.csv reviewed by domain expert
• DIC measurement types added to measurement_type.csv
• Ingest workflow implemented (extend ingest_calcofi_bottle.qmd or supplemental)
• Join to existing casts via cast_id or cruise+station+depth
• /validate-ingest passes
• Cross-dataset FKs validated
• Parquet exported & uploaded to GCS
• _targets.R updated
• release_database.qmd updated
• PR reviewed & merged

Dependencies

• Depends on: ingest_calcofi_bottle (uses existing bottle/cast PKs)
• Needed by: publish_dic_to_erddap

Replaces #6 and #19.