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/mi/counties/washtenaw/index.md

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

data/jurisdictions/us/states/mi/counties/washtenaw/municipalities/ann-arbor/people/christopher-taylor.md

@@ -0,0 +1,39 @@
+---
+type: Person
+title: "Christopher Taylor"
+description: "Mayor, Ann Arbor, MI"
+role: "Mayor, Ann Arbor, MI"
+level: "municipal"
+branch: "executive"
+state: "MI"
+tenure:
+  start: "2018-11-01"
+  current: true
+ids:
+  person: "4b90f4c6-86cf-4195-90f9-217c8c0e9cab"
+  office: "e2437767-e70e-4323-a0cb-ca3025a9a8f7"
+  tenure: "54d06a17-ce70-4bc9-a45f-b094b986caf4"
+  jurisdiction: "be4450fb-2ec2-4c06-acae-15929f8d3cc7"
+sources:
+  - field: office
+    source: "Wikidata"
+  - field: tenure
+    source: "Wikidata"
+  - field: jurisdiction
+    source: "Census TIGER 2024"
+confidence: official
+tags: [officeholder, municipal, executive, mi]
+timestamp: "2026-07-04"
+---
+
+# Christopher Taylor
+
+Current Mayor, Ann Arbor, MI.
+
+## Sources
+
+- office: Wikidata
+- tenure: Wikidata
+- jurisdiction: Census TIGER 2024
+
+Generated from the Atlas officeholders v3 export (2026-07-04).