feat(geo): use CF headers on opportunity map + country overview maps

Pre-select user's country on opportunity map dropdown (CF-IPCountry),
auto-load the map on page load. Highlight user's city on country
overview maps with a blue ring (CF-IPCity best-effort match). Unify
opportunity score color scale to red/amber/green (was using blue for
low scores). Inject window.__GEO global for client-side geo access.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -6,6 +6,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
 
+### Added
+- **Geo headers on city/region hubs** — Cloudflare geo headers (`CF-IPCountry`, `CF-IPCity`) now used across location-based pages. Opportunity map pre-selects and auto-loads the user's country. Country overview maps highlight the user's city with a blue ring (best-effort CF-IPCity name match). `window.__GEO` JS global injected via `base.html` for client-side map code.
+
+### Fixed
+- **Opportunity map color scale** — low-score bubbles used blue (`#3B82F6`) instead of red (`#DC2626`), inconsistent with the unified `scoreColor()` scale used everywhere else. Fixed in `oppColor()`, legend, and `article-maps.js` tooltip colors. Thresholds aligned to ≥60/30/\<30.
+
 ### Changed
 - **Opportunity Score v5 → v6** — calibrates for saturated markets (Spain avg dropped from ~78 to ~50-60 range). Density ceiling lowered from 8 → 5/100k (Spain at 6-16/100k now hits zero-gap). Supply deficit weight increased from 35 → 40 pts. Addressable market reduced from 25 → 20 pts. Market validation inverted → "market headroom": high country avg maturity now reduces opportunity (saturated market = less room for new entrants).
 - **Markets page map legend** — bubble map now has a visual legend explaining size = venue count, color = Market Score. Opportunity score tooltip color unified to same green/amber/red scale (was using blue for low scores, inconsistent).