fix: attribute shoreline addresses, and name the rows that cannot be placed

[keonik]

Migration 23 got 985,631 of 985,634 in production, then stopped:

3 row(s) still have no region after attribution: their coordinates fall outside
every US state boundary

Why three rows fail a containment test

TIGER state polygons stop at the waterline. A lakefront address, an island, a
pier — all sit outside every state polygon by a few metres while being
unambiguously in that state. Ohio has a Lake Erie shoreline, so this is the
expected shape of the remainder.

A second pass attributes from the nearest boundary within 500m. That is
comfortably wider than the waterline margin and far narrower than the distance
to another state, so it cannot silently move an address across a border.

Verified:

on-land    (-83.0, 40.0)      -> OH   well inside
shoreline  (-82.7, 41.7020)   -> OH   ~220m offshore, still Ohio
at-sea     (-40.0, 35.0)      -> ''   mid-Atlantic, a real error

Rows that still cannot be placed now identify themselves

Anything left is a coordinate error, not a missing state. The migration names
those rows in the error, not just the log:

1 row(s) still have no region: ... Offending rows:
  id=3 county=Unknown at (-40.0000, 35.0000)

That error is surfaced on /health, so whoever has to decide what to do with
them can see what they are without shell or database access. Diagnosing three
rows out of 5.8M should not require going to look for them.

If production's three turn out to be shoreline cases, this lands and migration
23 completes. If they are genuinely bad coordinates, /health will say exactly
where they are and we can delete or correct them deliberately.

🤖 Generated with Claude Code