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/hernando/people/mark-c-johnson.md

@@ -0,0 +1,39 @@
+---
+type: Person
+title: "Mark C. Johnson"
+description: "Hernando County School Board — Hernando County, FL"
+role: "Hernando County School Board"
+level: "county"
+branch: "legislative"
+state: "FL"
+tenure:
+  start: "2025-01-01"
+  current: true
+ids:
+  person: "cde2d542-af1b-46e1-9393-1ec559dd8703"
+  office: "98447a3b-0d3c-4d37-95b1-a7f6397caa2e"
+  tenure: "9b2805d2-cf6e-4fa9-8b21-16df9a00e78e"
+  jurisdiction: "82679068-adca-42d8-8806-e2655c72b550"
+sources:
+  - field: office
+    source: "FL Division of Elections"
+  - field: tenure
+    source: "FL Division of Elections"
+  - field: jurisdiction
+    source: "Census TIGER 2024"
+confidence: official
+tags: [officeholder, county, legislative, fl]
+timestamp: "2026-07-04"
+---
+
+# Mark C. Johnson
+
+Current Hernando County School Board (Hernando County, FL).
+
+## Sources
+
+- office: FL Division of Elections
+- tenure: FL Division of Elections
+- jurisdiction: Census TIGER 2024
+
+Generated from the Atlas officeholders v3 export (2026-07-04).