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/ne/districts/01.md

@@ -0,0 +1,59 @@
+---
+type: Jurisdiction
+title: "NE-01"
+classification: congressional-district
+state: "NE"
+district: "NE-01"
+demographics:
+  population: 672915
+  population_under_18: 178836
+  population_18_64: 235688
+  population_65_plus: 258391
+  median_household_income: 77659
+  poverty_rate: 11.33
+  homeownership_rate: 63.97
+  unemployment_rate: 3.05
+  median_home_value: 278400
+  gini_index: 0.4327
+  vacancy_rate: 4.28
+  race_white: 532635
+  race_black: 23116
+  race_asian: 19652
+  hispanic: 85129
+  bachelors_plus: 163226
+sources:
+  - field: demographics
+    source: Census ACS 2023
+confidence: official
+tags: [jurisdiction, congressional-district, ne]
+timestamp: "2026-07-03"
+---
+
+# NE-01
+
+Congressional district NE-01.
+
+## Demographics (ACS 2023)
+
+| Measure | Value |
+| --- | --- |
+| Population | 672915 |
+| Under 18 | 178836 |
+| 18–64 | 235688 |
+| 65+ | 258391 |
+| Median household income | 77659 |
+| Poverty rate | 11.33 |
+| Homeownership rate | 63.97 |
+| Unemployment rate | 3.05 |
+| Median home value | 278400 |
+| Gini index | 0.4327 |
+| Vacancy rate | 4.28 |
+| White | 532635 |
+| Black | 23116 |
+| Asian | 19652 |
+| Hispanic/Latino | 85129 |
+| Bachelor's or higher | 163226 |
+
+## Source
+
+- demographics: Census ACS 2023

data/jurisdictions/us/states/ne/districts/02.md

@@ -0,0 +1,59 @@
+---
+type: Jurisdiction
+title: "NE-02"
+classification: congressional-district
+state: "NE"
+district: "NE-02"
+demographics:
+  population: 682617
+  population_under_18: 191281
+  population_18_64: 239767
+  population_65_plus: 251569
+  median_household_income: 84478
+  poverty_rate: 10.97
+  homeownership_rate: 63.66
+  unemployment_rate: 4.08
+  median_home_value: 301500
+  gini_index: 0.4548
+  vacancy_rate: 5.21
+  race_white: 471857
+  race_black: 66498
+  race_asian: 29975
+  hispanic: 98471
+  bachelors_plus: 191861
+sources:
+  - field: demographics
+    source: Census ACS 2023
+confidence: official
+tags: [jurisdiction, congressional-district, ne]
+timestamp: "2026-07-03"
+---
+
+# NE-02
+
+Congressional district NE-02.
+
+## Demographics (ACS 2023)
+
+| Measure | Value |
+| --- | --- |
+| Population | 682617 |
+| Under 18 | 191281 |
+| 18–64 | 239767 |
+| 65+ | 251569 |
+| Median household income | 84478 |
+| Poverty rate | 10.97 |
+| Homeownership rate | 63.66 |
+| Unemployment rate | 4.08 |
+| Median home value | 301500 |
+| Gini index | 0.4548 |
+| Vacancy rate | 5.21 |
+| White | 471857 |
+| Black | 66498 |
+| Asian | 29975 |
+| Hispanic/Latino | 98471 |
+| Bachelor's or higher | 191861 |
+
+## Source
+
+- demographics: Census ACS 2023

data/jurisdictions/us/states/ne/districts/03.md

@@ -0,0 +1,59 @@
+---
+type: Jurisdiction
+title: "NE-03"
+classification: congressional-district
+state: "NE"
+district: "NE-03"
+demographics:
+  population: 649934
+  population_under_18: 165239
+  population_18_64: 194541
+  population_65_plus: 290154
+  median_household_income: 69788
+  poverty_rate: 10.3
+  homeownership_rate: 72.37
+  unemployment_rate: 3.04
+  median_home_value: 202300
+  gini_index: 0.4408
+  vacancy_rate: 9.58
+  race_white: 532309
+  race_black: 6497
+  race_asian: 5753
+  hispanic: 87924
+  bachelors_plus: 114057
+sources:
+  - field: demographics
+    source: Census ACS 2023
+confidence: official
+tags: [jurisdiction, congressional-district, ne]
+timestamp: "2026-07-03"
+---
+
+# NE-03
+
+Congressional district NE-03.
+
+## Demographics (ACS 2023)
+
+| Measure | Value |
+| --- | --- |
+| Population | 649934 |
+| Under 18 | 165239 |
+| 18–64 | 194541 |
+| 65+ | 290154 |
+| Median household income | 69788 |
+| Poverty rate | 10.3 |
+| Homeownership rate | 72.37 |
+| Unemployment rate | 3.04 |
+| Median home value | 202300 |
+| Gini index | 0.4408 |
+| Vacancy rate | 9.58 |
+| White | 532309 |
+| Black | 6497 |
+| Asian | 5753 |
+| Hispanic/Latino | 87924 |
+| Bachelor's or higher | 114057 |
+
+## Source
+
+- demographics: Census ACS 2023