docs: update changelog, CLI reference, user guide, and elevation notes

- CHANGELOG: document hysteresis elevation fix and DEM recalculation feature
- docs/reference/cli.md: add --dem-url to bincio edit and bincio serve tables
- docs/user-guide.md: document "Recalculate from terrain map" button in edit drawer
- docs/elevation.md: mark both short-term and medium-term fixes as implemented

docs/reference/cli.md

@@ -116,6 +116,7 @@ uv run bincio edit [OPTIONS]
 | `--port PORT` | `4041` | Bind port |
 | `--strava-client-id ID` | from config | Strava OAuth client ID |
 | `--strava-client-secret SECRET` | from config | Strava OAuth client secret |
+| `--dem-url URL` | `https://api.open-elevation.com` | Open-Elevation-compatible API for the "Recalculate elevation" button (also `DEM_URL` env var) |
 
 Set `PUBLIC_EDIT_URL=http://localhost:4041` in `site/.env` to enable the Edit button and Upload ↑ button in the site.
 
@@ -164,6 +165,7 @@ uv run bincio serve [OPTIONS]
 | `--site-dir DIR` | — | Astro site dir — enables post-write incremental rebuilds |
 | `--host HOST` | `127.0.0.1` | Bind address (keep on localhost; nginx proxies from outside) |
 | `--port PORT` | `4041` | Bind port |
+| `--dem-url URL` | `https://api.open-elevation.com` | Open-Elevation-compatible API for the "Recalculate elevation" button (also `DEM_URL` env var) |
 
 Requires `bincio init` to have been run first. Handles auth, user management, and write operations. nginx is responsible for serving static files and proxying `/api/*` to this server.