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/vt/districts/00.md

@@ -0,0 +1,59 @@
+---
+type: Jurisdiction
+title: "VT-00"
+classification: congressional-district
+state: "VT"
+district: "VT-00"
+demographics:
+  population: 648493
+  population_under_18: 132678
+  population_18_64: 198809
+  population_65_plus: 317006
+  median_household_income: 82730
+  poverty_rate: 9.02
+  homeownership_rate: 73.23
+  unemployment_rate: 2.67
+  median_home_value: 352800
+  gini_index: 0.4551
+  vacancy_rate: 16.79
+  race_white: 584330
+  race_black: 6276
+  race_asian: 13343
+  hispanic: 17401
+  bachelors_plus: 213912
+sources:
+  - field: demographics
+    source: Census ACS 2023
+confidence: official
+tags: [jurisdiction, congressional-district, vt]
+timestamp: "2026-07-03"
+---
+
+# VT-00
+
+Congressional district VT-00.
+
+## Demographics (ACS 2023)
+
+| Measure | Value |
+| --- | --- |
+| Population | 648493 |
+| Under 18 | 132678 |
+| 18–64 | 198809 |
+| 65+ | 317006 |
+| Median household income | 82730 |
+| Poverty rate | 9.02 |
+| Homeownership rate | 73.23 |
+| Unemployment rate | 2.67 |
+| Median home value | 352800 |
+| Gini index | 0.4551 |
+| Vacancy rate | 16.79 |
+| White | 584330 |
+| Black | 6276 |
+| Asian | 13343 |
+| Hispanic/Latino | 17401 |
+| Bachelor's or higher | 213912 |
+
+## Source
+
+- demographics: Census ACS 2023