fix: empty RT entity types

[davidgamez]

Summary:

Fixes #1847. GTFS-RT feeds with a blank entity type returned HTTP 500 on every access path, and broke any /v1/search page spanning them.

process_entity_types in api/src/scripts/populate_db_gtfs.py split the entity_type cell with "".split("-"), which returns [""] rather than []. The loop therefore ran once with an empty token and created Entitytype(name=""); the else branch was dead code. The generated models validate entity_types against the vp/tu/sa enum from DatabaseCatalogAPI.yaml, so a blank name failed serialization for the feed and for every unrelated feed on the same page.

Three layers:

• Populate script — new normalize_entity_types trims, lowercases, drops blanks, dedupes, and keeps only EntityType members (warn + skip otherwise). Entity types are replaced only when the normalized list is non-empty, preserving the existing "empty cell does not wipe" convention.
• Migration (liquibase/changes/fix_empty_entity_types.sql) — deletes blank entitytypefeed then entitytype rows, adds CHECK (name IN ('vp','tu','sa')), refreshes feedsearch.
• Tests — fixture rows for an empty cell, a padded/mixed-case cell (VP | sa), and a partly invalid cell (tu-bogus), plus a DB-wide assertion that no blank entity type names exist.

Expected behavior:

• GET /v1/search?data_type=gtfs_rt&limit=100&offset=0 no longer 500s.
• A blank, padded, or unknown entity_type cell in the catalog CSV produces no entitytype row; VP | sa yields ["vp","sa"], tu-bogus yields ["tu"] with a logged warning.
• INSERT INTO entitytype(name) VALUES ('') is rejected by the DB.

No public API surface change. Note: get_gtfs_rt_feeds_query inner-joins Entitytype, so the two fixed feeds stay out of the /v1/gtfs_rt_feeds list endpoint until they have real entity types (pre-existing behaviour, not changed here).

Testing tips:

# Apply the migration locally
docker compose --env-file ./config/.env.local up liquibase liquibase-test

# Constraint blocks bad names
docker exec database psql -U postgres -d MobilityDatabase \
  -c "INSERT INTO entitytype(name) VALUES ('');"   # expect: violates check constraint

# Only canonical names survive population
./scripts/docker-localdb-rebuild-data.sh --populate-db --populate-test-data
docker exec database psql -U postgres -d MobilityDatabase \
  -c "SELECT name, length(name) FROM entitytype;"  # expect only vp/tu/sa

./scripts/api-tests.sh

After deploy, confirm GET /v1/gtfs_rt_feeds/mdb-3438, mdb-3439, and a full-catalog paginated crawl of /v1/search?data_type=gtfs_rt.

• Run the unit tests with ./scripts/api-tests.sh to make sure you didn't break anything
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[davidgamez]

Changes in the operations API are missing updates from the previous PRs.

[cka-y]

LGTM

[cka-y]

👍