Define PNW geographic and metro-area scope

[Copilot]

What this changes

Defines the geographic model used to assess Pacific Northwest research candidates without introducing GIS infrastructure.

• Boundary: Washington, Oregon, Idaho, and British Columbia, with explicit exclusions and historical-place handling.
• Metro areas: Authority-backed membership, metro-level precision, and no boundary expansion.
• Research hints: Reviewed aliases, slang, regions, and features retained as evidence-routing metadata—not automatic qualification.
• Ambiguity: Unresolved, shared, and cross-boundary references require review.

Checklist

• Scoped to this change — no unrelated files swept in
• Directory README.md updated (or none needed)
• AGENTS.md updated if a working rule or convention changed

Playlist data

• Sources touched: none
• make check passes — not applicable (specification only)
• Overrides changed: none
  Every override edit records a human decision, not an inference
• publication-links.json entries come from real REST responses, not guessed IDs

Tooling

• make lint and make test pass — not applicable (specification only)
• A regression test covers any bug fixed in an override path, parser heuristic, or gate

Safety

• No secrets: no .env*, ~/.czarchive.toml, API keys, OAuth tokens, or cookies
• Superseded work moved to discarded/ with a README.md explaining why

• Fixes Define geographic boundary and metro-area handling. #77