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/nd/candidates/alex-balazs.md

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+---
+type: Candidate
+title: "Alex Balazs"
+description: "U.S. House candidate, ND-00 (2026)"
+office: "U.S. House"
+state: "ND"
+district: "ND-00"
+party: "REP"
+stance: "challenger"
+election_year: 2026
+status: "statutory candidate"
+committee:
+  name: "ALEX BALAZS FOR NORTH DAKOTA"
+  id: "C00933549"
+ids:
+  fec: "H4ND00079"
+sources:
+  - field: filing
+    source: FEC (Federal Election Commission)
+confidence: official
+tags: [candidate, federal, house, nd]
+timestamp: "2026-07-03"
+---
+
+# Alex Balazs
+
+Republican challenger for U.S. House (ND-00), 2026.
+
+## Campaign Committee
+
+- ALEX BALAZS FOR NORTH DAKOTA (C00933549)
+
+## Source
+
+- filing: FEC (Federal Election Commission)
+
+Federal candidate filing; not yet linked to an officeholder record.

data/jurisdictions/us/states/nd/candidates/julie-fedorchak.md

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+---
+type: Candidate
+title: "Julie Fedorchak"
+description: "U.S. House candidate, ND-00 (2026)"
+office: "U.S. House"
+state: "ND"
+district: "ND-00"
+party: "REP"
+stance: "incumbent"
+election_year: 2026
+status: "statutory candidate"
+committee:
+  name: "FEDORCHAK FOR ND"
+  id: "C00869370"
+ids:
+  fec: "H4ND00061"
+sources:
+  - field: filing
+    source: FEC (Federal Election Commission)
+confidence: official
+tags: [candidate, federal, house, nd]
+timestamp: "2026-07-03"
+---
+
+# Julie Fedorchak
+
+Republican incumbent for U.S. House (ND-00), 2026.
+
+## Campaign Committee
+
+- FEDORCHAK FOR ND (C00869370)
+
+## Source
+
+- filing: FEC (Federal Election Commission)
+
+Federal candidate filing; not yet linked to an officeholder record.

data/jurisdictions/us/states/nd/candidates/trygve-hammer.md

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+---
+type: Candidate
+title: "Trygve Hammer"
+description: "U.S. House candidate, ND-00 (2026)"
+office: "U.S. House"
+state: "ND"
+district: "ND-00"
+party: "DEM"
+stance: "challenger"
+election_year: 2026
+status: "statutory candidate"
+committee:
+  name: "HAMMER FOR ND"
+  id: "C00935494"
+ids:
+  fec: "H6ND01049"
+sources:
+  - field: filing
+    source: FEC (Federal Election Commission)
+confidence: official
+tags: [candidate, federal, house, nd]
+timestamp: "2026-07-03"
+---
+
+# Trygve Hammer
+
+Democratic challenger for U.S. House (ND-00), 2026.
+
+## Campaign Committee
+
+- HAMMER FOR ND (C00935494)
+
+## Source
+
+- filing: FEC (Federal Election Commission)
+
+Federal candidate filing; not yet linked to an officeholder record.