docs: update CHANGELOG with error pages and map improvements

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

CHANGELOG.md

@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
 
+### Added
+- **Custom 404/500 error pages** — styled error pages extending `base.html` with i18n support (EN/DE). The 404 page is context-aware: when the URL matches `/markets/{country}/{city}`, it shows a city-specific message with a link back to the country overview instead of a generic "page not found".
+- **Map: city article indicators** — country overview map bubbles now differentiate cities with/without published articles. Cities without articles appear in muted gray and are not clickable, preventing dead-end navigations. The `/api/markets/<country>/cities.json` endpoint includes a `has_article` boolean per city.
+
 ### Fixed
 - **Admin template preview maps** — Leaflet maps rendered blank because `article-maps.js` called `L.divIcon()` at the IIFE top level before Leaflet was dynamically loaded, crashing the script. Moved `VENUE_ICON` creation into the `script.onload` callback so it runs after Leaflet is available. Previous commit's `.card` `overflow: visible` fix remains (clips tile layers otherwise).
 - **Admin articles page 500** — `/admin/articles` crashed with `BuildError` when an article generation task was running because `article_stats.html` partial referenced `url_for('admin.article_stats')` but the route didn't exist. Added the missing HTMX partial endpoint.