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/sc/counties/oconee/index.md

@@ -32,7 +32,7 @@ timestamp: "2026-07-03"
 
 # Oconee County, SC
 
-County jurisdiction.
+County jurisdiction — 1 officeholders mapped.
 
 ## Demographics (ACS 2023)
 

data/jurisdictions/us/states/sc/counties/oconee/municipalities/seneca/people/daniel-w-alexander.md

@@ -0,0 +1,39 @@
+---
+type: Person
+title: "Daniel W. Alexander"
+description: "Mayor, Seneca, SC"
+role: "Mayor, Seneca, SC"
+level: "municipal"
+branch: "executive"
+state: "SC"
+tenure:
+  start: "2026-06-20"
+  current: true
+ids:
+  person: "46c1e9b2-5649-4ad8-9c0f-c2cdce84aa77"
+  office: "1d583285-9cc2-4b6c-bafb-c36fbb25508f"
+  tenure: "51108437-6919-4b17-86c5-5b0d0314759a"
+  jurisdiction: "ffb76177-73f5-4f2a-850b-dd912121a696"
+sources:
+  - field: office
+    source: "Wikidata"
+  - field: tenure
+    source: "Wikidata"
+  - field: jurisdiction
+    source: "Census TIGER 2024"
+confidence: official
+tags: [officeholder, municipal, executive, sc]
+timestamp: "2026-07-04"
+---
+
+# Daniel W. Alexander
+
+Current Mayor, Seneca, SC.
+
+## Sources
+
+- office: Wikidata
+- tenure: Wikidata
+- jurisdiction: Census TIGER 2024
+
+Generated from the Atlas officeholders v3 export (2026-07-04).