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/wa/districts/03.md

@@ -0,0 +1,59 @@
+---
+type: Jurisdiction
+title: "WA-03"
+classification: congressional-district
+state: "WA"
+district: "WA-03"
+demographics:
+  population: 802855
+  population_under_18: 187411
+  population_18_64: 259843
+  population_65_plus: 355601
+  median_household_income: 92354
+  poverty_rate: 7.99
+  homeownership_rate: 69.64
+  unemployment_rate: 5.15
+  median_home_value: 506700
+  gini_index: 0.4259
+  vacancy_rate: 6.8
+  race_white: 613469
+  race_black: 16987
+  race_asian: 30562
+  hispanic: 98055
+  bachelors_plus: 173215
+sources:
+  - field: demographics
+    source: Census ACS 2023
+confidence: official
+tags: [jurisdiction, congressional-district, wa]
+timestamp: "2026-07-03"
+---
+
+# WA-03
+
+Congressional district WA-03.
+
+## Demographics (ACS 2023)
+
+| Measure | Value |
+| --- | --- |
+| Population | 802855 |
+| Under 18 | 187411 |
+| 18–64 | 259843 |
+| 65+ | 355601 |
+| Median household income | 92354 |
+| Poverty rate | 7.99 |
+| Homeownership rate | 69.64 |
+| Unemployment rate | 5.15 |
+| Median home value | 506700 |
+| Gini index | 0.4259 |
+| Vacancy rate | 6.8 |
+| White | 613469 |
+| Black | 16987 |
+| Asian | 30562 |
+| Hispanic/Latino | 98055 |
+| Bachelor's or higher | 173215 |
+
+## Source
+
+- demographics: Census ACS 2023