Node detail "Heard By": the Regions line and Region column read a field the endpoint does not emit

[efiten]

public/nodes.js builds two pieces of the "Heard By" card from o.iata:

• nodes.js:781 — a Regions: line above the heading, [...new Set(observers.map(o => o.iata).filter(Boolean))]
• nodes.js:790 — a Region column header, with data-sort-key="region"

/api/nodes/{pubkey}/health emits neither. The rows are HealthObserverRow (cmd/server/direct_heard.go:54-61) and carry exactly observer_id, observer_name, avgSnr, avgRssi, packetCount, can_relay. Confirmed against a running instance:

{"observer_id":"47F9548F…","observer_name":"BE-DUF-SiSCD-01",
 "avgSnr":6.65,"avgRssi":-110.88,"packetCount":8596,"can_relay":null}

So the Regions line never renders (filter(Boolean) empties the set) and the Region column prints an em dash on every row, including its sort control.

This is pre-existing and was named in #2057 ("It also documented an iata field on these rows that the endpoint has never emitted; removed" and "both have always been dead"), where it was correctly left out of scope. Filing it so it does not stay a remark in a merged description: the card was just rewritten, and it still ships a column that cannot hold a value and a sort key that cannot order anything.

Either direction is fine, they just need deciding

1. Drop them. Remove the Regions line, the Region header and its data-sort-key. Smallest change, and the information is available on the observers page.
2. Emit the field. Add ObserverIATA string \json:"observer_iata"`toHealthObserverRow and read that name in the template. The value is already joined in the query the builder walks (COALESCE(obs.iata, '')` appears in the observation queries), so this is plumbing rather than new data. Worth it only if per-observer region actually helps on this card — with direct lists now holding a handful of rows, grouping them by region may not.

Whichever is chosen, the fix should include an assertion in tests/unit/test-direct-rf-heard-by.js, which slices this exact template out of nodes.js and so can pin it.

Not investigated: whether other cards read o.iata off endpoints that do emit it under a different name. enrichObsWithTx uses observer_iata, so the mismatch may be a naming drift rather than a one-off.