Update lakeflag for misclassified reaches

[jameshgrn]

Update lakeflag values after island-in-lake fix. Blocked by #17.

[jameshgrn]

Update: Validation GUI (#75) now supports lakeflag fixes:

• C001 tab: Convert river→lake for lake sandwiches
• C004 tab: Fix lakeflag/type mismatches

Both tabs include satellite imagery, skip reasons, and local persistence.

[jameshgrn]

Lake Sandwich Correction Complete (v17c)

1,252 reaches corrected — river reaches (lakeflag=0) sandwiched between lake reaches, reclassified to lakeflag=1.

Detection Criteria

• Width: sandwich width >= 50% of the wider neighboring lake
• Length: sandwich shorter than at least one neighboring lake reach
• Both upstream AND downstream neighbors must be lakeflag=1

Changes Applied

• lakeflag → 1
• type → copied from wider lake neighbor (mostly type=3)
• edit_flag → appended lake_sandwich for traceability

Regional Breakdown

Region	Count
NA	548
AS	344
EU	161
SA	143
AF	43
OC	13

Not Corrected (requires manual review)

• Narrow sandwiches (width < 50% of lakes): ~732 — high FP rate, many are genuine connecting channels
• Chain sandwiches (2+ consecutive river reaches between lakes): ~949 pairs — need separate approach
• Wide + longer than both lakes: ~170 — mixed confidence

Synced to

• DuckDB: data/duckdb/sword_v17c.duckdb ✅
• PostgreSQL: reaches table ✅

Review files

• output/facc_detection/lake_sandwich_wide_shorter_one.geojson (the 1,252 corrected)
• output/facc_detection/lake_sandwich_high_confidence.geojson (956 subset: shorter than both lakes)