Show the tree's file names without the .geojson suffix

The suffix ("ride.gpx" -> "ride.gpx.geojson" once cached) explained
what the name would download back when it doubled as a GeoJSON-only
download link. Now that downloading is the download button's job
(previous commit), it was just confusing -- the file itself is still
named "ride.gpx".

docs/architecture.adoc

@@ -338,18 +338,18 @@ app, and not yet opened. Badging the common case would just be noise,
 so the file tree's icon (`PENDING_ICON`, `public/js/icons.js`) marks
 that exception instead of the (near-universal) ready state.
 +
-Once a `.gpx`/`.fit` is cached, the tree shows it under its converted
-name instead — `"ride.gpx"` reads as `"ride.gpx.geojson"`, matching
-the real cache file sitting next to it on disk — since the GeoJSON,
-not the original, is what's actually rendered on the map from that
-point on. Plain text now, not a link — see below. The original is
-never deleted or re-parsed once cached, just not re-shown as itself,
-so both forms need a way out of the app as an actual file: one
-download button, next to delete, opens a small menu ("Original file" /
-"GeoJSON", `_downloadButton`/`_downloadMenuItem`) rather than the name
-doubling as a GeoJSON-only download link the way it briefly did — that
-was easy to miss as a link at all, and only ever covered half of
-what's downloadable. Only one menu open at a time
+The tree always shows a `.gpx`/`.fit` file under its real, as-uploaded
+name, even once cached — it briefly grew a `.geojson` suffix there
+(matching the real cache file's name on disk) back when the name
+doubled as a GeoJSON-only download link and the suffix explained what
+clicking it would get you; now that downloading is the download
+button's job (below), the suffix was just confusing; the file itself
+is still named `"ride.gpx"`. The original is never deleted or
+re-parsed once cached, just not re-shown as itself once the GeoJSON
+becomes what's actually rendered on the map, so both forms need a way
+out of the app as an actual file: one download button, next to
+delete, opens a small menu ("Original file" / "GeoJSON",
+`_downloadButton`/`_downloadMenuItem`). Only one menu open at a time
 (`_toggleDownloadMenu`/`_closeDownloadMenu`), closed by a
 document-level click listener the same way an outside click closes a
 `sidebar-flyout` dropdown, just scoped to this one control rather than