fix(settings): stop offering a column the backend rejects

Settings -> Track List Columns listed two rows both called "Track
Name", one of which could not be ticked, and a screen reader heard
"Show the Track Name column" twice with nothing to tell them apart.

They are `titleArtist` and `trackName`, and the issue left open which
way to fix it: a second label so the sort dropdown and the configurator
can say different words, or drop the row because the user cannot select
it. The code settles that. `titleArtist` is not in
`tracklist.AllColumnIDs`, so `Config.Validate()` returns `unknown
track-list column ID: "titleArtist"` -- ticking the row sends a column
set the backend rejects, `config-page` swallows the rejection into a
`console.error`, and the tick reverts. A second label would have named
a control that cannot work.

So a definition says whether it is a *choice*, and the configurator
reads `CONFIGURABLE_COLUMN_IDS` rather than `Object.keys(COLUMN_DEFS)`.

The new test reads Go's own list out of `backend/tracklist/config.go`
rather than writing it down a third time, since a third copy is the
fault one step earlier. Verified by planting: with the filter removed
all four assertions fail with the defect's own numbers.

Not fixed here, and filed as #231: `SetTrackListColumns` assigns before
it validates, so a rejected list stays in memory and `Save()` validates
the whole config -- one tick and no setting saves for the rest of the
session. That is reachable from any invalid input, not from this row.

Closes #197

CLAUDE.md

@@ -3275,6 +3275,27 @@ its own duplicates apart) — and changing either is invisible against an
 existing `YJ_HOME`, whose `config.toml` already holds the old list, so
 `make sandbox-seed NAME=default` before believing the app.
 
+**And the *valid* columns are declared twice too, which is the pair
+that drifted.** `tracklist.AllColumnIDs` is what the backend accepts;
+`COLUMN_DEFS` is what the frontend knows how to draw, and they are not
+the same set — `titleArtist` is a definition and not a choice, since it
+is the phone's stacked column and is picked by width in
+`PHONE_COLUMN_IDS`. Settings built its list from `Object.keys(
+COLUMN_DEFS)` and so offered it: **two rows both called "Track Name"**
+(#197), the second unselectable, because ticking it sends a column set
+Go rejects with `unknown track-list column ID` and `config-page`
+swallows that into a `console.error`. `CONFIGURABLE_COLUMN_IDS` is what
+the configurator reads now, derived from a `configurable` flag on the
+definition, and `settings-column-list.test.ts` reads Go's own list out
+of the source rather than writing it down a third time — the rule being
+about every column, so checking one checks nothing.
+
+One thing it does **not** fix, because it is reachable from any invalid
+input rather than from that row: `SetTrackListColumns` assigns before it
+validates, so a rejected list stays in memory and `Save()` validates the
+whole config — one tick and **no setting saves for the rest of the
+session**, silently. That is #231.
+
 **Event-driven communication**: Backend emits events via Wails runtime; frontend stores subscribe to them. Event names are constants in `backend/events/`.
 
 `frontend/src/events.ts` is **generated** from `backend/events/events.go`