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/nc/districts/05.md

@@ -0,0 +1,59 @@
+---
+type: Jurisdiction
+title: "NC-05"
+classification: congressional-district
+state: "NC"
+district: "NC-05"
+demographics:
+  population: 755224
+  population_under_18: 173326
+  population_18_64: 232854
+  population_65_plus: 349044
+  median_household_income: 59041
+  poverty_rate: 15.85
+  homeownership_rate: 66.21
+  unemployment_rate: 4.2
+  median_home_value: 245700
+  gini_index: 0.4808
+  vacancy_rate: 12.6
+  race_white: 527244
+  race_black: 128426
+  race_asian: 18837
+  hispanic: 63323
+  bachelors_plus: 148115
+sources:
+  - field: demographics
+    source: Census ACS 2023
+confidence: official
+tags: [jurisdiction, congressional-district, nc]
+timestamp: "2026-07-03"
+---
+
+# NC-05
+
+Congressional district NC-05.
+
+## Demographics (ACS 2023)
+
+| Measure | Value |
+| --- | --- |
+| Population | 755224 |
+| Under 18 | 173326 |
+| 18–64 | 232854 |
+| 65+ | 349044 |
+| Median household income | 59041 |
+| Poverty rate | 15.85 |
+| Homeownership rate | 66.21 |
+| Unemployment rate | 4.2 |
+| Median home value | 245700 |
+| Gini index | 0.4808 |
+| Vacancy rate | 12.6 |
+| White | 527244 |
+| Black | 128426 |
+| Asian | 18837 |
+| Hispanic/Latino | 63323 |
+| Bachelor's or higher | 148115 |
+
+## Source
+
+- demographics: Census ACS 2023