Municipals: nest 1,823 city officeholders under their real counties

Pull Atlas's place→county crosswalk (Census TIGER 2024 places × county
geometries, 32,041 places) into the build as a committed raw input, and
use it to resolve municipal officeholders whose county was unknown.

- data/place_county_crosswalk.jsonl — new raw input (place_geoid → county_geoid)
- build.py — place-name+state → county_geoid → ACS county slug as a fallback
  in county_slug(); city_slug() generalized to non-FL bare place labels
- data/sources/sources.yaml — provenance entry for the crosswalk

_unresolved municipals: 1919 → 58. The remainder are genuine: CT planning
regions (post-county), county-level rows mislabeled municipal upstream,
consolidated city-counties (null label), Wikidata-QID placeholder names,
and ambiguous same-name places — left unresolved rather than guessed.

Join key is county_geoid (5-digit FIPS); the directory slug is taken from
the ACS county node so municipals nest under the exact existing county dir.
Deterministic (byte-identical rebuild); validate.py passes 19,721 records.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

data/jurisdictions/us/states/sd/counties/brookings/index.md

@@ -32,7 +32,7 @@ timestamp: "2026-07-03"
 
 # Brookings County, SD
 
-County jurisdiction.
+County jurisdiction — 2 officeholders mapped.
 
 ## Demographics (ACS 2023)
 

data/jurisdictions/us/states/sd/counties/brookings/municipalities/brookings/people/oepke-ope-niemeyer.md

@@ -0,0 +1,39 @@
+---
+type: Person
+title: "Oepke \"Ope\" Niemeyer"
+description: "Mayor, Brookings, SD"
+role: "Mayor, Brookings, SD"
+level: "municipal"
+branch: "executive"
+state: "SD"
+tenure:
+  start: "2021-05-01"
+  current: true
+ids:
+  person: "6738b494-e31c-4d47-a1b1-e4a0f868bd80"
+  office: "b9f72c02-f865-43c2-98b2-434555241c15"
+  tenure: "d0ed9829-6931-4e2b-b724-431599440d75"
+  jurisdiction: "780b7e06-7c7f-4534-ba5b-534e22907681"
+sources:
+  - field: office
+    source: "Wikidata"
+  - field: tenure
+    source: "Wikidata"
+  - field: jurisdiction
+    source: "Census TIGER 2024"
+confidence: official
+tags: [officeholder, municipal, executive, sd]
+timestamp: "2026-07-04"
+---
+
+# Oepke "Ope" Niemeyer
+
+Current Mayor, Brookings, SD.
+
+## Sources
+
+- office: Wikidata
+- tenure: Wikidata
+- jurisdiction: Census TIGER 2024
+
+Generated from the Atlas officeholders v3 export (2026-07-04).

data/jurisdictions/us/states/sd/counties/brookings/municipalities/volga/people/ken-fideler.md

@@ -0,0 +1,39 @@
+---
+type: Person
+title: "Ken Fideler"
+description: "Mayor, Volga, SD"
+role: "Mayor, Volga, SD"
+level: "municipal"
+branch: "executive"
+state: "SD"
+tenure:
+  start: "2026-06-20"
+  current: true
+ids:
+  person: "e7724625-e5dc-4919-92ec-76fc3c2e7747"
+  office: "f26ba60e-e6bd-486c-9e2d-ea8a28e32c9a"
+  tenure: "7f75e8bc-518b-4717-98e0-d87212310d1d"
+  jurisdiction: "f35c6383-e297-4457-af99-f4d4bb497501"
+sources:
+  - field: office
+    source: "Wikidata"
+  - field: tenure
+    source: "Wikidata"
+  - field: jurisdiction
+    source: "Census TIGER 2024"
+confidence: official
+tags: [officeholder, municipal, executive, sd]
+timestamp: "2026-07-04"
+---
+
+# Ken Fideler
+
+Current Mayor, Volga, SD.
+
+## Sources
+
+- office: Wikidata
+- tenure: Wikidata
+- jurisdiction: Census TIGER 2024
+
+Generated from the Atlas officeholders v3 export (2026-07-04).