Add elections + demographics layer: candidates and jurisdictions

Two new entity types, built deterministically from the raw exports:

  Candidate (2,494)     — 2026 federal candidates as files under
                          us/states/<st>/candidates/, with office,
                          district, party, incumbent/challenger stance,
                          campaign committee, FEC id.

  Jurisdiction (3,494)  — demographic nodes carrying ACS 2023 data:
                          3,131 counties (deduped from 3,231 mixed-format
                          fips keys) + 363 congressional districts.

This completes the county skeleton nationwide: every US county is now a
browsable node with population, income, poverty, race, education and
housing — even where no officeholders are mapped yet. In Florida the
county index.md merges into the existing dir and reports its officeholder
count alongside demographics (St. Lucie: 33 officeholders + ACS profile).

build.py now reads seven raw inputs in one deterministic pass
(byte-identical on rerun). The mirror now answers: who holds power, who
runs this institution, who is running, and what each place is made of.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

data/jurisdictions/us/states/nj/counties/hudson/index.md

@@ -0,0 +1,61 @@
+---
+type: Jurisdiction
+title: "Hudson County, NJ"
+classification: county
+fips: "34017"
+state: "NJ"
+demographics:
+  population: 718323
+  population_under_18: 141994
+  population_18_64: 485536
+  population_65_plus: 90793
+  median_household_income: 91795
+  poverty_rate: 14.93
+  homeownership_rate: 30.72
+  unemployment_rate: 6.01
+  median_home_value: 539700
+  gini_index: 0.5046
+  vacancy_rate: 6.63
+  race_white: 231594
+  race_black: 85703
+  race_asian: 122062
+  race_native: 7051
+  hispanic: 292607
+  bachelors_plus: 360526
+sources:
+  - field: demographics
+    source: Census ACS 2023
+confidence: official
+tags: [jurisdiction, county, nj]
+timestamp: "2026-07-03"
+---
+
+# Hudson County, NJ
+
+County jurisdiction.
+
+## Demographics (ACS 2023)
+
+| Measure | Value |
+| --- | --- |
+| Population | 718323 |
+| Under 18 | 141994 |
+| 18–64 | 485536 |
+| 65+ | 90793 |
+| Median household income | 91795 |
+| Poverty rate | 14.93 |
+| Homeownership rate | 30.72 |
+| Unemployment rate | 6.01 |
+| Median home value | 539700 |
+| Gini index | 0.5046 |
+| Vacancy rate | 6.63 |
+| White | 231594 |
+| Black | 85703 |
+| Asian | 122062 |
+| Native | 7051 |
+| Hispanic/Latino | 292607 |
+| Bachelor's or higher | 360526 |
+
+## Source
+
+- demographics: Census ACS 2023