R1: schema & naming reset — squash migrations, rename variants

Squash the 12 goose migrations into one 00001_baseline.sql (there is no prod
data; verified schema-identical to the chain via a pg_dump diff + the green
integration suite) and rename the game-variant labels
english/russian_scrabble/erudit -> scrabble_en/scrabble_ru/erudit_ru across the
backend, the FlatBuffers wire values and the UI.

dawg filenames and the Go enum identifiers are unchanged; the i18n display keys
are kept. Adds PRERELEASE.md (the R1-R7 pre-release tracker), linked from
CLAUDE.md. Contour DB wipe and the scrabble-dictionary tidy are follow-ups.

ui/src/lib/codec.ts

@@ -325,7 +325,7 @@ export function decodeProfile(buf: Uint8Array): Profile {
 export function decodeStateView(buf: Uint8Array): StateView {
   const v = fb.StateView.getRootAsStateView(new ByteBuffer(buf));
   const g = v.game();
-  const variant = (g ? s(g.variant()) : 'english') as Variant;
+  const variant = (g ? s(g.variant()) : 'scrabble_en') as Variant;
   // Cache the alphabet table when the server included it (a per-variant cache miss), then
   // decode the index rack to display letters with it (Stage 13).
   if (v.alphabetLength() > 0) {
@@ -681,7 +681,7 @@ export function decodeGcg(buf: Uint8Array): GcgExport {
 function emptyGame(): GameView {
   return {
     id: '',
-    variant: 'english',
+    variant: 'scrabble_en',
     dictVersion: '',
     status: '',
     players: 0,