Fix note UX: unreachable wiki link, white Save hover, stale icon preview, invisible new points

- "Nearby on Wikipedia" linked to KIWIX_URL, a Docker-internal hostname
  (http://kiwix:8080) no real browser can resolve. Split it: KIWIX_URL
  stays server-side-only for the reachability check, and the link
  itself is built from KIWIX_PUBLIC_PORT (kiwix-serve's newly
  published host port) plus whatever host the visitor already used to
  reach maptool — works regardless of which hostname/IP that is.
- The Save button went white on hover in GTK-themed Chrome: the
  browser's native button skin was painting over the custom
  background because appearance wasn't reset.
- The map preview marker for a pending note always showed a plain red
  pin no matter which icon was picked in the form. NoteSaveForm now
  reports icon changes via onIconChange so NotesControl can update the
  marker's glyph live.
- Saving a note (or a Measure "Save as note") left the new/grown
  .geojson file unchecked and invisible until manually toggled on.
  notifyGpxStoreChanged now carries the affected path so
  GpxPanelControl auto-shows it.

docs/development.adoc

@@ -77,11 +77,16 @@ outline rather than a single point).
 A point popup's "Nearby on Wikipedia" link needs
 https://github.com/kiwix/kiwix-tools[kiwix-serve] running with a
 Wikipedia https://library.kiwix.org[ZIM] loaded — set `KIWIX_URL` to
-wherever it's reachable (`docker-compose.yaml` already runs a `kiwix`
-service pointed at `data/kiwix/wikipedia.zim` and wires `KIWIX_URL` to
-it; blank/unset disables the link, same as every other optional
-integration here). Not part of the repo — a ZIM is a large,
-self-contained archive, obtain one locally:
+wherever *the server* can reach it (`docker-compose.yaml` already runs
+a `kiwix` service pointed at `data/kiwix/wikipedia.zim` and wires
+`KIWIX_URL` to it via its compose service name; blank/unset disables
+the link, same as every other optional integration here). This is
+used only for the server-side reachability check — a browser can't
+resolve a Docker-internal hostname like `kiwix`, so the link itself is
+built from `KIWIX_PUBLIC_PORT` (the host port kiwix-serve is
+`ports:`-published on, `8090` in `docker-compose.yaml`) plus whatever
+host the visitor already used to reach maptool itself. Not part of the
+repo — a ZIM is a large, self-contained archive, obtain one locally:
 
 * https://library.kiwix.org/#lang=eng&category=wikipedia[Kiwix's own
   library] has pre-built Wikipedia ZIMs — a `_maxi` variant per