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/wi/districts/05.md

@@ -0,0 +1,59 @@
+---
+type: Jurisdiction
+title: "WI-05"
+classification: congressional-district
+state: "WI"
+district: "WI-05"
+demographics:
+  population: 750363
+  population_under_18: 166485
+  population_18_64: 223689
+  population_65_plus: 360189
+  median_household_income: 91909
+  poverty_rate: 6.83
+  homeownership_rate: 74.04
+  unemployment_rate: 2.54
+  median_home_value: 386200
+  gini_index: 0.4289
+  vacancy_rate: 4.84
+  race_white: 647909
+  race_black: 12948
+  race_asian: 23556
+  hispanic: 52385
+  bachelors_plus: 226308
+sources:
+  - field: demographics
+    source: Census ACS 2023
+confidence: official
+tags: [jurisdiction, congressional-district, wi]
+timestamp: "2026-07-03"
+---
+
+# WI-05
+
+Congressional district WI-05.
+
+## Demographics (ACS 2023)
+
+| Measure | Value |
+| --- | --- |
+| Population | 750363 |
+| Under 18 | 166485 |
+| 18–64 | 223689 |
+| 65+ | 360189 |
+| Median household income | 91909 |
+| Poverty rate | 6.83 |
+| Homeownership rate | 74.04 |
+| Unemployment rate | 2.54 |
+| Median home value | 386200 |
+| Gini index | 0.4289 |
+| Vacancy rate | 4.84 |
+| White | 647909 |
+| Black | 12948 |
+| Asian | 23556 |
+| Hispanic/Latino | 52385 |
+| Bachelor's or higher | 226308 |
+
+## Source
+
+- demographics: Census ACS 2023