Sync: officeholders v3 — fresh export from live Atlas DB (13,329 tenures)

Re-exported directly from Postgres (10.0.0.116), not Atlas's introspection,
which under-reported the roster (its v3 export had 11,473, missing the
restored Florida League of Cities municipal set). Live DB current tenures:
state 7,561 · municipal 4,009 · county 1,217 · federal 542.

- build.py now reads officeholders-v3.jsonl (was v2); dataset vintage 2026-07-04
- fixed one corrupt start_date at source-export (21021-12-03 -> 2021-12-03,
  Lorraine Borowski, Mayor of Decorah IA)
- scripts/build_viz.py: committed, deterministic generator for the Board's
  county_data.json / county_detail.json (previously built ad-hoc)
- generate_changelog.py: ignore files whose only change is the vintage stamp,
  so the diff reflects government change, not re-export bookkeeping

Person files 11,285 -> 13,329. Non-FL municipal officials (1,903) are in the
tree but not yet county-mappable (place->county crosswalk still NULL).

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

data/jurisdictions/us/states/fl/counties/flagler/people/donald-o-brien.md

@@ -0,0 +1,42 @@
+---
+type: Person
+title: "Donald O'Brien"
+description: "Commissioner, Flagler County — Flagler County, FL"
+role: "Commissioner, Flagler County"
+level: "county"
+branch: "legislative"
+state: "FL"
+contact:
+  email: "dobrien@flaglercounty.gov"
+  phone: "(386) 313-4093"
+tenure:
+  start: "2025-01-01"
+  current: true
+ids:
+  person: "1198c774-d45f-4d51-90e2-f6afe7a2964e"
+  office: "7ec01798-0b03-47c9-b014-57a7278da87a"
+  tenure: "40f00ef8-df3a-4844-a930-9771b4c59703"
+  jurisdiction: "b072bcd4-3e05-4584-9564-92b936024900"
+sources:
+  - field: office
+    source: "Florida Association of Counties"
+  - field: tenure
+    source: "Florida Association of Counties"
+  - field: jurisdiction
+    source: "Census TIGER 2024"
+confidence: official
+tags: [officeholder, county, legislative, fl]
+timestamp: "2026-07-04"
+---
+
+# Donald O'Brien
+
+Current Commissioner, Flagler County (Flagler County, FL).
+
+## Sources
+
+- office: Florida Association of Counties
+- tenure: Florida Association of Counties
+- jurisdiction: Census TIGER 2024
+
+Generated from the Atlas officeholders v3 export (2026-07-04).