feat(launcher): add sync command to merge stats and history between machines over SSH

subminer sync <host> exchanges VACUUM INTO snapshots over ssh/scp and each
side merges the other's data as an insert-only union keyed on session UUIDs,
video keys, series title keys, and word/kanji identity. Lifetime totals and
daily/monthly rollups are applied incrementally so pre-retention history
survives, remote-only historical rollups are copied, and re-syncing is
idempotent. sync --snapshot/--merge expose the underlying steps for manual
transfers; a pid-file/mpv-socket guard refuses to run while SubMiner may be
writing the database and schema-version mismatches abort the merge.

launcher/main.ts

@@ -22,6 +22,7 @@ import { runLogsCommand } from './commands/logs-command.js';
 import { runStatsCommand } from './commands/stats-command.js';
 import { runJellyfinCommand } from './commands/jellyfin-command.js';
 import { runHistoryCommand } from './commands/history-command.js';
+import { runSyncCommand } from './commands/sync-command.js';
 import { runPlaybackCommand } from './commands/playback-command.js';
 import { runUpdateCommand } from './commands/update-command.js';
 
@@ -107,6 +108,10 @@ async function main(): Promise<void> {
     return;
   }
 
+  if (runSyncCommand(context)) {
+    return;
+  }
+
   const resolvedAppPath = ensureAppPath(context);
   state.appPath = resolvedAppPath;
   log('debug', args.logLevel, `Using SubMiner app binary: ${resolvedAppPath}`);