refactor: remove unused knobs, strings and stale text

Drop what nothing uses any more: the --max-syllables flag with its
sourceSpec field, meta row and reject reason; the store's clearRejection;
the --gap CSS token; three orphaned i18n strings; two exports with no
importer; the preview npm script; the proto.yml "baseline exists" step
that has been unconditionally true since the schema landed on main; and
two root-level .gitignore entries for paths Playwright never writes.

Correct text that outlived its subject: NOTICE named a tools/ directory
that never existed, the README still pointed at the first plan and
carried a migration note for retired sources, and a few comments still
said "release" for an upstream that is a weekly export. The pin test
header now says three copies and also holds README and ATTRIBUTION to
the same URL; the Make-targets table lists clean and help.

Wire fixtures regenerated so client_hello uses the ProtocolVersion
constant and server_game_started carries the 30s turn limit.
builder_version becomes 4 for the dropped meta row.

web/src/lib/i18n/vi.js

@@ -34,12 +34,10 @@ export const t = {
 	you: 'Bạn',
 	opponent: 'Đối thủ',
 	someone: 'Người chơi',
-	scoreLabel: 'Điểm',
 	syllableUnit: 'tiếng',
 	correctedFrom: 'Bạn gõ “{typed}”, từ đúng là “{word}”.',
 
 	secondsLeft: '{n} giây',
-	waiting: 'Đang chờ…',
 	connecting: 'Đang kết nối…',
 	connected: 'Đã kết nối',
 	reconnecting: 'Mất kết nối, đang thử lại…',
@@ -77,7 +75,6 @@ export const t = {
 	copyLink: 'Sao chép liên kết mời',
 	shareLink: 'Chia sẻ',
 	copied: 'Đã sao chép',
-	waitingForOpponent: 'Đang chờ người chơi vào phòng…',
 	leaveRoom: 'Rời phòng',
 	shareInvite: 'Vào chơi nối từ với tôi',
 

web/src/lib/stores/game.svelte.js

@@ -492,9 +492,6 @@ export function createGameStore() {
 			);
 		},
 
-		clearRejection() {
-			state.rejection = null;
-		},
 		clearError() {
 			state.error = null;
 		},

web/src/lib/ws/client.js

@@ -39,7 +39,7 @@ export const LIVENESS_TIMEOUT_MS = 3 * PING_INTERVAL_MS;
  * client reconnects every half second forever after a deploy that bumps the
  * protocol.
  */
-export const TERMINAL_ERROR_CODES = new Set(['protocol_version_mismatch']);
+const TERMINAL_ERROR_CODES = new Set(['protocol_version_mismatch']);
 
 const RESUME_KEY = 'noitu.resumeToken';