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/commands/playback-command.test.ts

@@ -36,6 +36,13 @@ function createContext(): LauncherCommandContext {
       texthookerOpenBrowser: false,
       useRofi: false,
       history: false,
+      sync: false,
+      syncHost: '',
+      syncSnapshotPath: '',
+      syncMergePath: '',
+      syncRemoteCmd: '',
+      syncDbPath: '',
+      syncForce: false,
       logLevel: 'info',
       logRotation: 7,
       passwordStore: '',